Edging Sanity: A Sapphic Erotic Thriller

by Kestrel Martin

What would you do if an infamous serial killer set her sights on breaking you?

Rowan Aberdeen is head of security at Raven Wood Psychiatric Facility. She’s used to dealing with the dangerous and mentally unstable. Receiving patients from the penitentiary in town is a run of the mill process. Standard procedure. Until one miraculous plea of insanity and Delilah Watson—the deadliest serial killer their facility has ever known—is transferred and placed under Rowan’s direct supervision.

Within days, one glaring fact of Rowan’s new situation becomes Delilah has fixated on her. Rowan’s sole focus now revolves around controlling Delilah’s obsession and manipulating it to her advantage. Especially when it becomes clear that Delilah is used to getting what she wants. And she will stop at nothing to get Rowan.

156 pages, Kindle Edition

Expected publication September 24, 2026

Reviews

[Bridie · Rating 5 out of 5]

I… need more of this book immediately.

Rowan? Hot as fuck. Delilah? Hot as fuck. Insane? Both of them.

I love Kestrels writing. She’s written this book in a way that really makes you feel like your sanity is being edged… in the best way possible.

Enter this book with the knowledge that you’ll only want more…

[Jae Alistar · Rating 5 out of 5]

(In)Sanity Has Never Tasted So Delicious

Edging Sanity is a wickedly twisted and deeply addictive sapphic thriller that feeds on obsession, psychological tension, and the ever-blurring line between sanity and madness. Between revenge, murder, psychological games, and twist after twist, this book keeps tightening the screws until you’re left questioning who is actually in control. The title perfectly captures the psychological spiral (and the increasingly smoldering spice) as it increasingly toes that dangerous line.

Rowan is already battling her own demons before Delilah ever enters the picture, but her pursuit of Delilah soon becomes an increasingly consuming fixation. Delilah is an incredibly intelligent, thoroughly unhinged serial k*ller with a twisted sense of justice who targets truly horrible people while remaining utterly unpredictable. As Rowan becomes increasingly drawn to Delilah, Delilah is slowly unraveling Rowan’s past and learning exactly how to get under her skin. The more they recognize themselves in each other, the more dangerous their games become.

Their fascination with one another is consuming from the start, and the tension only escalates as Delilah keeps pushing Rowan to break the rules. Rowan thinks she’s in control, but it becomes increasingly clear that Delilah has been pulling the strings all along. Every interaction pushes Rowan further and further towards finding out just how far she’s willing to go. With their mutual infatuation-turned-obsession, and an absolutely carnal lust, their desire is literally dripping off the pages.

This definitely isn’t a romance—it’s an addiction that neither woman seems particularly interested in escaping. The twists and turns kept me guessing right up until the end and made this exactly the kind of thriller to leave you questioning who was ever really in control. Edging Sanity keeps you teetering right alongside Rowan on that knife’s edge between obsession and madness. Disturbing, destructive, and beautifully deranged, Kestrel absolutely committed to the chaos here.

Thank you to the author for the chance to read this ARC!

Favorite Quotes:
“She was a serial killer, a certified genius, diagnosed psychopath, and, unfortunately, painfully attractive.”

“I do understand what society deems right and wrong. I just disagree with some of it. I have my own preferences, and I don’t particularly care what others think of that.”

“I don’t want you obsessed with me. I want you addicted. Obsessions die. They don’t last. But addiction? It alters your brain chemistry and sinks its claws into you and never lets you go. It’ll always be there, lingering in the back of your mind.”

“Where adrenaline should be ratcheted up, there were only thoughts of [her]. She was a woman possessed.”

“Your pleasure, your pain. They belong to me. You belong to me.”

[BookaholicallyBridie · Rating 5 out of 5]

I was delighted to receive an ARC of this book from the author. Here is my honest review:

My sanity was edged so hard it fell off a cliff and went splat on the ground.

Rowan and Delilah are both iconic and completely terrifying. I adore them both. The relationship between them is so deranged, and also hot as hell. Everything Delilah did only made me love her more.

I must confess, I found Delilah a little too relatable at times (send help).

There was an absolutely exquisite plot twist that completely blew my mind and I loved it.

If you want a completely psychotic sapphic thriller, you NEED to read this one.

[Emma · Rating 5 out of 5]

got this book as an arc in exchange for an honest review 💞💞 thank you a lot for this one!!! 🥰

kestrel martin i need to know what the actual FUCK goes on in your brain because there is genuinely NOTHING this woman cannot do 😭😭😭 A FUCKING GEEENIUS I'M LIKE SUCH A FAN GIRL- 😭😭😭😭

edging sanity was SO. FUCKING. GOOD.
like… psychiatric facility. infamous serial killer. head of security. obsession. manipulation. psychological warfare. spice. women being absolutely fucking insane.

HELLO????? LIKE ARE WE OKAYYYY-

and the craziest part is that i genuinely don't think i've ever read anything quite like this before?? the whole concept felt so new and refreshing to me and i was hooked SO fast. the plot just kept moving and shifting and throwing things at me and i swear i could not foreshadow a SINGLE FUCKING THING. every time i thought i knew where we were going- YEAH I DID NOT KNOW WHERE WE ARE GOING.

and the third person pov??? GENIUS. ACTUALLY GENIUS.

because we don't get to crawl inside everyone's head and know exactly what they're thinking. we don't get all the little internal clues that usually let you piece together what's coming. instead we're stuck watching these women from the outside and trying to figure out what the fuck they're doing along with everyone else. which i usually dont enjoy too much because i want to know EVERYTHING about the characters BUT IT JUST WORKED SOOOOOOOO WELL WITH THIS BOOK SERIOUSLY I CANT IMAGINE IT DIFFERENTLY 😭😭😭😭😭

and DELILAH????? yeah well.. DELILAH WATSON YOU ABSOLUTELY INSANE WOMAN.

she is terrifying in the most delicious way possible. watching her fixation on rowan develop was SO fucking interesting because you never really know how far she's willing to go until she just… goes further. and further. and further.

BUT CAN WE TALK ABOUT ROWAN?????

because everyone is like “oh my god delilah is insane” and i'm sitting here like
are we SURE rowan is okay???? girl WHAT ARE YOU DOING???? 😭😭😭

the things she does and the choices she makes had me questioning her sanity just as much as delilah's. at some point i genuinely wasn't sure who i was supposed to be afraid of anymore and honestly???

i LOVED that.

and the spice?????
oh. my. fucking. god.

the chemistry??? the tension??? the absolute fucking insanity of these two??? yes please and thank you. the spice was SO good and it fit into the story perfectly instead of feeling like it was randomly shoved in. we got our thriller AND our sapphic insanity AND our spice. truly a woman of the people.

and the pacing???? SO GOOD.
i genuinely did not want this book to end. every time i thought “okay maybe i'll stop here” something else happened and suddenly i'm like NOPE ONE MORE CHAPTER and then i'm staring at the ceiling questioning my life choices.

kestrel martin has such a fucking way with storytelling. AND STORY INVENTING?????

there's something about her books that makes me completely lose myself in them. she knows how to build tension, how to make characters feel unpredictable, how to keep me guessing, and most importantly how to make me sit there going WHAT THE FUCK IS HAPPENING while somehow still being completely obsessed.

my only little 👁️👁️ with this one is the ending... because WHAT DO YOU MEAN WE'RE JUST LEAVING ME HERE?????
there are SO. MANY. QUESTIONS. i finished this book with like seventeen theories, twelve unanswered questions, three conspiracy boards and absolutely zero peace of mind 😭😭😭 i don't even necessarily hate an open/ambiguous ending, but… you have left me with THOUGHTS. so. many. thoughts. and i fear my brain is going to be chewing on this for a while. but overall???

kestrel martin, you have done it again.
i will literally pick up anything this woman writes because apparently i enjoy having my sanity stolen by fictional women. 😋

thriller? fucking yes.
spice? FUCKING YES.
unhinged women? YESSSSS.
a plot i couldn't predict for the life of me? ABSOLUTELY.

my sanity? unfortunately gone.

5 stars for the experience of being absolutely fucking played by this book 😭😭😭😭😭

[Gwin Savage · Rating 5 out of 5]

Whew! I don’t even know where to begin. I went in prepared for a wild ride, but still found myself whispering “what the fuck?” and feverishly DMing the author every other chapter.

Trying to look back on the book to write this review is a blur of scorching tension and insanity—and I mean this in the best possible way. Edging Sanity was like a fever dream that I devoured in the course of a weekend, never quite knowing what would happen next and finding my jaw dropping at every revelation.

Delilah is a serial killer whose personality leaps off the page. She’s requested a transfer to Raven Wood Psychiatric Facility from prison and proceeds to be an absolute diabolical handful as she fixates on Rowan from the moment they meet. Rowan is such an interesting character to me. (I mean, they both are for sure!) She’s the epitome of the saying “still waters run deep.” On the surface she appears to be stoic, strong, and in-control as Raven Wood’s head of security and Delilah’s personal escort around the facility. But there’s far more to her than meets the eye.

Where Delilah wears her darkness like a badge of honor, Rowan’s dark past trickles out in enticing hints and splashes that left me always wanting more. She falls into her addiction to Delilah in the most intoxicating and all-consuming ways that I didn’t see coming… but it all made a strange sort of sense by the end!

Erotic thriller indeed! The driving force behind the story are the two FMCs and the positively titillating cat-and-mouse that springs up between them. The spice is some of the most creative and intense I’ve read in quite some time. Rowan and Delilah’s chemistry is evident from the jump and only gets more wildly out of control as the book goes on. The ending is shocking and satisfying in the most toxic way that had me kicking my feet and squealing because these two nut cases definitely deserve each other!

[Lauren · Rating 5 out of 5]

From the beginning you can feel the sexual tension between Rowan and Delilah. Delilah is a brat and trying to make Rowan break the rules.

So these two will immediately put you in a chokehold and you will want to keep reading and never stop. It’s spicy it’s chaotic it’s unhinged it draws you in so easily. So Rowan likes to toy with Delilah too. There’s so much back and forth.

Delilah has clearly done her research prior to coming to this facility. She knows too much. She’s starting to realise how similar her and Rowan are and it just adds to the back and forth tension arising. It’s written in such a way that the tension lifts off the screen and pulls you in.

So Delilah takes touch her and die to the extreme and it’s wonderful to read. The ownership, the possessiveness, the way they are addicted to each other.

This definitely is not a romance it’s an addiction that neither one of them wants to escape. Feelings don’t matter in this unhinged relationship because they will simply do anything for each other because they are addicted to one another.

I would highly recommend this book to anyone who want like a dose of unhinged lesbians. Kestrel Martin has made you fall in love with the unhinging and has made you want to crave more. If you want a cozy romance this is not the book for you. If you want unhinged chaos look no further because I promise you this book has exactly that. Very spicy very brilliant can’t wait to see what Kestrel has in store for her next books.

[Mel's Sapphic Reviews · Rating 5 out of 5]

This was my first ever ARC and damn was it a great one to begin my ARC journey! Just wanna say a quick thank you to Kestrel for allowing me to be a part of your team and for gifting us with this absolutely crazy (literally) amazing book!

For starters, this is such a hot, erotic, and immensely alluring book. What could be better than a thriller with sexy, obsessive, dangerous lesbians?! Also, you're going to fall in love with Delilah. Don't fight it. Just know it'll happen. 😇 OH, and you probably won't know if you want to be with Rowan or just BE Rowan. I'm thinking the answer is both. BUT also... am I ok??? Is it ok to enjoy this book so much?

All jokes aside, I really liked how this book had the vibes of girls protecting girls in a way. It was vague just like the implication of SA, but ultimately it was a major detail that stuck with me and made me really understand and like the characters more. No matter how demented they really are.

This book had so many twists and turns that I didn't see coming and made me just gawk at the page for a few seconds. I'm one of those people who always thinks they know what's gonna happen next (I'm right like 90% of the time 😂) but I DID NOT KNOW the true unhinged insanity that was about to go down on each page. You will definitely finish this book in one go. And then you will question what the hell just happened. BUT like in the best way. Because Kestrel is brilliant. Highly recommend, go get your sanity edged!

[Katie B · Rating 5 out of 5]

I. Am. OBSESSED! I absolutely devoured this in less than 24 hours. Could NOT stop reading. Delilah.. why is psychotic always so sexy? I was around 33% through when I realised I was already absolutely obsessed with her. I was surprised with Rowan as well but I can’t say more than that without spoilers. I NEED MORE OF THEM!
At the start, there was something that didn’t quite make sense to me. However, it absolutely makes sense after the last third of the book and makes me want to reread it instantly. There’s probably much more eloquent things to say about this but I’m just on such a reading high right now I don’t have more words. LOVE.

Plot Summary.
Delilah is a bit of a psychotic serial killer, who has wormed her way into a psychiatric facility instead of prison. Rowan, is head of security and personally assigned to escort Delilah to and from her therapy sessions. An obsession begins, and there’s some wonderful twists along the way..

Things I Loved:
- Delilah. Obviously.
- The therapist
- Rowan’s past
- The ending
- The lawyer
- The spice
- Mental health rep
- Knife play
- Getting her claws into Rowan
- Literally everything

Overall, it’s just bloody wonderful really. Femme serial killer and masc head of security, a dangerous obsession, forced proximity, and not knowing who you can trust. YES!!!

Check content warnings.
Massive thank you to the author for a free ARC in return for honest review.

[LezLibros · Rating 5 out of 5]

This is such a deliciously dark and unhinged read!! I loved every single page. Edging Sanity is written so well! The storyline is disturbing, the characters are anything but lovable, but still… I loved this book!!! While this is a chaotic story, the connection between Delilah and Rowan is clearly felt and almost feels tender in an obsessive sort of way. Maybe I think that because I need professional help (don’t worry, I’m getting it!), but this book is more than killing and obsession and deranged madness. It’s a creepy psychotic love story between two women who have questionable morals and sick desire. And the spicy scenes are crazy as fuck… but SO HOT!!! I loved the way the author revealed bits and pieces of Rowan’s history through the story. There’s so many twists and turns that you really can’t stop reading until the very end. It’s like if you took a contemporary sapphic romance, twisted it until it’s hardly recognizable, and mated it with a dark thriller romance - this is the result, and it’s fucking awesome. Please do pay attention to the content warning, and read at your discretion.

[Mourning Star · Rating 5 out of 5]

Well, my sanity was indeed edged.

Having read Cost of Vices and loving Bellamy and Vesper, I figured I'd end up loving Delilah and Rowan as well.

I was right, but at what cost?

I finished ES the same day I got the ARC. I inhaled this thing. I sat there, somewhat disgusted at times and then immensely satisfied at others.

It's been about thirty minutes since I've finished and my hands are still a little shaky. I probably need a snack because I feel a little queasy, too.

These lesbians are toxic. This is not a romance. This is not even remotely dark romance. This is horror. It's a horror/thriller with obsession, mania, and insanity.

And it's insanely hot. Every page is filled with perverse, deranged thoughts that simply work. It's the type of book that about halfway through you think, "is the author okay?"

I have very little else to say besides the following quote:

"Delilah Watson was a serial killer, a certified genius, diagnosed psychopath, and, unfortunately, painfully attractive."

[C.L. Smoke · Rating 5 out of 5]

THIS IS NOT A ROMANCE. It is toxic. Unhinged. Obsession. Everything that should make sane people run for the hills. You will question your sanity when you finish this book, but in the best way.

Okay. Okay. Listen...I will do questionalble things for Delilah Watson and maybe I need to have my sanity checked. I think I have a type and it's unhinged, psychotic femmes who can kill me, but it's fine. I will fall to my knees for Delilah proudly.

I already knew going into this it would be delicious and unhinged. AND BOY DID KESTREL DELIVER. I devoured this book. Delilah HOT!! Rowan?? You're a smart woman and also hot. The spice??? Delicious, Devine, Intense, and very questionable. I loved every moment of this intense ride. And there was a nice little plot twist that I loved.

If you love unhinged lesbians, intense power dynamics, and a hot butch who gets on her kness?? you'll LOVE this erotic thriller. Question your sanity and dive in.

[Rowan Womble · Rating 5 out of 5]

"Delilah Watson was a serial killer, a certified genius, diagnosed psychopath, and, unfortunately, painfully attractive."

I inhaled this entire text in a grand total of three hours. That's how enthralled I was.

Obsession, possession, addiction. The serial killer "romance" trifecta—I honestly felt two of those three as a reader.

As someone named Rowan, this was a weird read. But also really good! Pretty tame as far as an erotic thriller goes, but I have seen some things, so maybe that's just me.

There's nothing quite like watching a vicious killer break the butch security guard she's ensorcelled with her feminine wiles. It'd work on me, tbh.

I'd let Delilah do whatever she wanted to me—please don't tell my girlfriend I said that.

The spicy bits might make a weaker woman squeamish, as fair warning, but if you don't mind a little bit of a sharp touch, 10/10, would recommend.

[Hailey Watkins · Rating 5 out of 5]

Why was this written in a way where MY sanity was being questioned? I was on the edge of my seat the entire book, it was insane.

Rowan and Delilah are both crazy people who are genuinely meant to be together. I was only sad that we didn’t get MORE of them. I wanted more conversations, more scenes, more explanations. Being in Rowan’s consciousness was so devilishly fun.

I didn’t expect all the little twists in the story, so bravo for that. More please????

The puzzle pieces of the story fit together so teasingly slow. Kestrel Martin was edging the audience as much as her characters did to each other.

Very happy to have been an ARC reader! Would give this 4.75 stars rounded up. Wish I could better articulate my feelings for the story but I’m so dumbfounded by how much I loved it. Quick, nearly psychological, read with a decent amount of spice.

[Jade Ford · Rating 4 out of 5]

I'm a big fan of Kestrel Martin's work, and this book matched my expectations beautifully! Edging Sanity is a deliciously dark thriller featuring a sapphic relationship between two characters that are complex and exciting to follow. It was fun to read of a blossoming relationship between two characters that were far from sweet, but equally matched in their darkness. The erotic elements of the novel was beautifully balanced with the plot, meaning when seduction did happen, it was exciting and you felt that it happened for a reason. There were some artistic license with how a prison runs, but I thought overall that the characters were plausible and the story engaging.

Once again, Kestral has delivered a beautiful story with a bite - taking well-known themes and delivering that something a tiny bit darker, but that you can still relate to. I would happily recommend it!

[Jules ♡ · Rating 5 out of 5]

Edging Sanity by Kestrel Martin - NOT a romance. Or maybe it is. Find out for yourself I guess (it's really not). This book will leave you feeling all sorts of things.

So happy I received the Arc, I ate this up and I need MORE

Delilah (HOT) and Rowan (HOT) are unhinged and toxic and f*cked up. Don't read this and expect a cute love story. Or a love story at all. Obsession, M*rder, Lies...
It 's HOT and shocking and you might need therapy after. Kestrel did an amazing job with this story, it's 10/10 all around. The story, the smut, the characters! Also a Plot twist. Who doesn't like those?? Go read this sapphic, sick and deranged story!

[Marina · Rating 5 out of 5]

Well, that was feral.

I thoroughly enjoyed the dark elements of this book. The author does an excellent job making the main characters complex but still relatable… even if one is a serial killer, you kind of want to forgive her.

I have so much I want to say about this book, but I don’t want to give anything away because it is absolutely worth your time to read. Dark, obsessive, intense, sexy, gory. And both main characters are hot as hell. Ex army butch security and leggy red head dom femme?

The book is well written and flows well. The pacing is great and I found there to be very few lulls in the storytelling.

Delilah is absolutely insane and wild. I love her.

[J. Tobias · Rating 5 out of 5]

This is definitely one of those books where you ask yourself what the fuck did I just read?! I consider my sanity sufficiently edged!
This book was hot, intense, edgy and I couldn't put it down!
Both characters were manipulative and complex and I couldn't help but fall for the beautiful, complicated serial killer.
Although it's a quick read, I felt like I really got to know the characters and rooted for their insane, unconventional pairing.
The spice was off the charts 🔥!
The story was so compelling, I read it in one sitting!
If you love your women morally dark, unhinged and hot af, this is the story for you.

A huge thank you to Kestrel for allowing me to read an ARC of this book!

[Sarah · Rating 4 out of 5]

4.5 ⭐️
I really enjoyed this ARC. The storyline was totally different to other dark romance that I’ve read. I loved Rowan and her and Delilah’s dynamic and obsession with each other. It was dark, hot and intriguing, keeping me wanting to read on (finished it in one sitting). One spicy scene in particular was 👀 👀 👀! (If you’ve read it I’m sure you know the one I mean!)

I’d love for there to be an epilogue novella to see what continues to happen after.

I am definitely interested in reading more by this author.

[jade! · Rating 5 out of 5]

advance review copy received from author
⭐️⭐️⭐️⭐️⭐️
this is the type of book that had me sat and devouring it all in one sitting. Kestrel says this isn’t a romance, but i’d beg to differ in saying it’s actually the most deranged thrilling romance story ever. Delilah and Rowan are utterly enthralled with each other. there is nothing that is capable of keeping them apart. it’s toxic and dangerous and so so addicting to read. i somehow managed nearly 40 highlights in just 176 pages, and had to restrain myself from highlighting entire chapters, literally.

[Katie Scott-Howells · Rating 4 out of 5]

ARC graciously received from the author!

BIIIIIG, fat 4.5 stars!!

At first, while I was reading, I thought “man this is kinda cold and emotionless” and then it dawned on me, DUH! This is literally a book about two psychopaths lol. Once that little revelation washed over me, I appreciated the complexity of the story and the little tidbits of back story that were sprinkled in. I think this was a fun and interesting, albeit, unhinged story of two people’s mutual obsession. The ONLY thing that kept this from being 5 stars… I’m a big slut and it could’ve had more spice 🤷🏼‍♀️ sue me

[E Michael · Rating 3 out of 5]

I received an advance reader copy at no charge. This is my honest and voluntary review.

A sapphic erotic thriller that delivers a twisty mix of pleasure and palpable danger. A toxic ride between a serial killer, who is always two steps ahead, and the butch head of security who struggles not to be intrigued by her.

The most compelling part for me was the ending, when everything came together. Would have loved the chance to peek into the future and see where the ruinous attraction took both of them.

[Sarah S. · Rating 4 out of 5]

Grateful to have gotten the ARC for this from the author! I am discovering that I do love a prison/inmate theme, and this fits that bill.

We have Rowan, our guard, and Delilah, our serial unaliver that gets moved to a psych facility for potential rehabilitation.

The two become infatuated with each other and it becomes a push and pull between them until they both finally give in.

The spice was excellent! The story was really good. I loved the twist! But the ending didn’t feel right to me.

Overall, I really enjoyed it and would recommend.

[Tenley Hale · Rating 5 out of 5]

Received an ARC for this & finished in one day! This was a wild ride but I enjoyed it. I won’t spoil too much but I loved that the serial killer goes after child predators. There is obviously a lot of spice in this but I also liked hearing some about the main character’s backstories & the little therapy sessions. Would have loved an epilogue or a second book to this!

[Hayleigh King · Rating 5 out of 5]

You will finish this book and be disappointed it's over. The characters are well written albeit insane and the writing is so well done you feel like you are right there with them. A story of lust and obsession that you will not forget.

[Kassie Bates · Rating 4 out of 5]

Well,

Delilah wasn’t even as crazy as Rowan 😂 didn’t see that coming.
The ending wasn’t my favorite i will say, but i enjoyed the book. The strap scene was SO HOT. I think the book gained a whole star more just for that 🤭😅

3.5⭐️

[SunshineReads23 · Rating 5 out of 5]

Absolutely 5 stars.

*will give full review when released