Not My Sister

by Rosie Walker

A girl stands on the doorstep, her hands tremble and her eyes glisten with tears. My sister has finally come home after six long years.

I gasp in disbelief when I meet my younger sister’s gaze. I can’t believe I’m looking at Lydia’s sweet face again. We’d been so close as children. Then one day she didn’t come home from school, and she disappeared without a trace.

Having Lydia back at home is the best thing that’s happened in years. Only I can’t shake the feeling that something isn’t right. She doesn’t remember any of the stories I tell about our childhood, she’s even forgotten her long bouts of illness. When I ask about the day she vanished, she says she doesn’t recall what happened.

I want to be close to my sister again more than anything. But when I find a strange message hidden in her room, I begin to suspect the girl who came home isn’t my sister at all. Who is she? And what really happened to Lydia?

I’m convinced I’m living with an impostor. And I will stop at nothing to expose the truth…

An absolutely gripping and addictive psychological thriller that will keep you turning the pages until late into the night. If you love The Housemaid, Gone Girl or The Other Daughter, you’ll adore Not My Sister.

Readers love Rosie
‘Had me in a hold from the first page… I devoured it in less than 24 hours! Full of twists and turns… Loved it!’ NetGalley reviewer ⭐️⭐️⭐️⭐️⭐️

‘From the moment I picked this book up, I was hooked… I even stayed up late reading… I loved it!… My favourite… The ending was one WOW!’ Arcreviews_by_m ⭐️⭐️⭐️⭐️⭐️

‘Wowsers… Just wowsers! I really was blown away! I absolutely did not see that twist coming.’ Jsybookworm ⭐️⭐️⭐️⭐️⭐️

‘Addictive. I finished it in one day because I just couldn’t put it down.’ B for bookreview ⭐️⭐️⭐️⭐️⭐️

‘Comes at you with both barrels and knocks you out of your shoes!’ Goodreads reviewer ⭐️⭐️⭐️⭐️⭐️

‘Oh my god!… Absolutely thrilling! Full of twists and turns. My jaw was hanging open.’ Jessicasbookbiz ⭐️⭐️⭐️⭐️⭐️

367 pages, Paperback

Expected publication March 4, 2026

About the author

Rosie Walker is a novelist who lives in Edinburgh with her husband, daughter, and dog. She has published four novels: 'Secrets of a Serial Killer', 'The House Fire', 'The Baby Monitor' and 'My Husband's Ex'.

Her next book, 'The Bride's Secret', is coming in 2025.

Rosie has a Masters in Creative Writing from the University of Edinburgh and an undergraduate degree in Psychology from Lancaster University.

Reviews

[Mikayla Larlee · Rating 4 out of 5]

Not My Sister is dark, emotional, and pretty intense. The first half was a little slow and frustrating for me, but once the big reveal hit, I was completely hooked. The pacing picked up, the tension ramped way up, and the twists really landed. I also appreciated how respectfully the mental health themes were handled. Overall, a gripping and surprisingly emotional read.

Thank you NetGalley for the ARC

[Kelsey Nicole · Rating 4 out of 5]

4.5 ⭐️

I absolutely loved this. It was so twisty! Every time I thought we’d hit the big reveal, something even bigger happened and completely blew my mind. The story flowed really well and kept me hooked the whole way through. The characters were messy and flawed in the best way, which made everything feel more real. I loved Annabel from the very start and was always rooting for her — I really felt for her. Such a gripping read, I couldn’t put it down and loved every minute of it. The only reason it didn’t get the full 5 stars for me was because I wish we had a bit more at the end and learned more about what happened afterwards.

I can’t wait to rave about this when it’s out. I think thriller lovers are gonna eat this up!!!

Thank you bookouture & NetGalley for the early arc copy!!

[Lupita_333 · Rating 3 out of 5]

3.5 stars

Predictable story from the beginning but still super well written and drawn out.

Unrealistic in so many aspects.

Oblivious characters. I wanted so badly to be able to scream at certain characters to just call the cops and run already. There were so many obvious things that it’s shocking how they weren’t put to pieces together. So frustrating but in a good way!

Twisted and malicious character who made me fear for the other characters. I got chills when I realized the extent of their evil.

Thank you NetGalley for the ARC in exchange for an honest review.

[Kayleigh Ann · Rating 4 out of 5]

ARC from NetGalley 📖

🌟 🌟 🌟 🌟

• Loads of twists
• Never knew which characters to trust
• 100% recommend for thriller fans

Will definitely be reading more by Rosie Walker👻

[Janna (Bibliophile Mom) · Rating 4 out of 5]

Not My Sister is a dark, gripping, and emotional story about two sisters. One who mysteriously disappeared six years ago, and the other who was left behind to navigate life with their mother and estranged father. I genuinely enjoyed this book, although I’ll be honest: the first half almost threw me off. Wendy’s naivety (the mum) was hard to ignore, especially when Annabel kept voicing her doubts about Lydia’s sudden reappearance after so many years. Annabel herself also felt a little overworked as a character early on, almost as if she was trying too hard to convince the reader of her perspective.

But once I reached the halfway point, everything shifted. The major revelation hit me, and from that moment I was completely hooked. The pacing tightened, the tension escalated beautifully, and the author delivered the twists with precision. I also appreciated how thoughtfully the mental health themes were taken into the narrative. These were handled with sensitivity and respect, adding depth without feeling exploitative. Every character carried their own flaws, traumas, and emotional baggage, which made the story feel raw, genuine, and surprisingly moving.

What I enjoyed:
• The alternating first‑person narration that kept the story dynamic
• The sensitive and realistic portrayal of mental health struggles
• A shocking twist that genuinely elevated the entire reading experience

What didn’t sit right:
• One character’s naivety that made me flinch more than once
• Another character’s desperation that occasionally felt forced or exaggerated
• Dark themes that may be triggering or uncomfortable for some readers

Ratings Breakdown:
• Setting: 3⭐️
• Characters: 3⭐️
• Writing: 4⭐️
• Message: 4⭐️
• Overall: 4⭐️

Overall, I highly recommend this twisty, emotionally charged thriller. I honestly thought I’d end up disappointed, but once the story found its rhythm, I was fully invested right up to the final page. Each character is wrestling with their own pain and history, and that messy emotional landscape fuels the chaos in a compelling way. Huge thanks to NetGalley, Bookouture, and author Rosie Walker for the advance copy.

~JaNnA~

[Els · Rating 4 out of 5]

When your younger sister leaves for school one day and then disappears, your world is turned upside down. Every day you hope she will be found. Together with your mother, you put up posters and go out searching. She tries to keep people aware through the internet and encourages them to stay alert. As if that weren’t bad enough, there are two other important factors that keep the worry alive.

Until one day, your sister suddenly appears on the doorstep. Six years have passed by then.

It goes without saying that she has changed, and it’s understandable that she first wants some time to rest and recover.

Days go by, and the suspicion that this young woman might not be your sister at all grows stronger and stronger.

So it becomes time to find out what exactly happened on that tragic day.

I have to admit that along the way I noticed certain clues in the book that led me to draw conclusions which, surprisingly enough, later turned out to be correct. That didn’t bother me at all.

On the contrary—it can actually be quite nice to figure something out once in a while.

The only downside I could mention is the somewhat slow pace, at least for me. It does pick up later on, which made it more enjoyable to read and easier to get swept away by the story.

All in all, a good story with a few shocking revelations. 4 stars.

Thank you.

[Tashie_LeeReads · Rating 4 out of 5]

Overall ⭐️⭐️⭐️⭐️/5


This is one of those books that quietly pulled me in before completely flipping everything I thought I understood. Going into it, I’ll admit I wasn’t immediately hooked. The beginning felt a little slow and draggy. But in hindsight, that careful build-up is exactly what makes the payoff so crazy.

Every time I felt confident about what was happening, another twist happened and threw me for a loop. Rosie masterfully plays with perception, making you question not only the characters but also your own instincts as a reader and I love when that happens.

What truly stood out about this book is its ability to keep me guessing. The twists and turns weren't just surprising, they genuinely disoriented me in the best way, leaving me wondering whether I ever really understood what was going on in the first place.

It’s the kind of book that made me want to go back and reread earlier chapters just to catch the clues I missed.

I can't wait to read more by this author :)

[Barbara Schultz · Rating 4 out of 5]

Title: Not My Sister
Author: Rosie Walker
Publisher: Bookouture
Genre: Psychological Thriller
Pub Date: March 4, 2026
My Rating: 4.3 Stars
Pages: 367

This story is about sisters- Lydia and Annabel.
Lydia mysteriously disappeared when she was thirteen; leaving her nineteen year old sister Annabel and their mother Wendy shattered.

Story starts six years later, when Lydia suddenly appears at the front door. Wendy assumes she is one of Annabel’s friends. However, she announces she is Lydia and has come home. Wendy doesn’t recognize her based on the age progression done by the Missing Person’s Department but does recognize a mole on her jawline.
However when Annabel comes home she has doubts - even their dog Max a miniature Schnauzer doesn’t recognize her. Mac and Lydia were once inseparable. Additionally Lydia doesn’t remember what happened plus doesn’t remember any of the stories Annabel shares about their childhood or the long illness they both had it appears all her memories are lost.

Lydia’s lack of memory is bothering Wendy so she decides to talk about her mother and her childhood. She tells Lydia about how awful it was when she was twelve and lost her twin brother Mariusz. He drowned and it tore apart the family.
This, of course, is new to Lydia.

Annabel grows increasingly convinced that this girl is not her sister.
Who is she? And what really happened to Lydia?

This is only my second Rosie Walker and I look forward to reading another.
When I read Ex-Girlfriend my comment was
The Big Reveal was a surprise!! I went into this without any expectations and it was great!!

Which is how I feel about this story.

I was curious about the Ms. Walker’s ' motivation and she tells us in “A Letter from Rosie Walker”
First she tells us that writing this was a rollercoaster; in fact the final story is very different from her original idea.
Her inspiration was based on a true story of Nicholas Barclay
- I don’t want to give too much away so if interested, I suggest you read it!

to thank NetGalley and Bookouture for this early eGalley.
Publishing Release Date scheduled for March 4, 2026.

[Leanne · Rating 4 out of 5]

Not My Sister is one of those thrillers that grabs you from the very first page and refuses to let go. The premise alone is deliciously unsettling—a missing sister returns after six years, but nothing about her feels quite right—and the tension only builds from there.

The story is told with a wonderfully claustrophobic sense of doubt. You can feel the narrator’s hope and heartbreak tangled together as she tries to reconnect with Lydia, only to be met with blank memories, strange behaviour, and a growing sense that the girl standing in front of her might not be who she claims to be. That creeping unease is handled so well; every chapter adds just enough suspicion to keep you turning pages.

What really works is the emotional core. This isn’t just a mystery—it’s a story about grief, longing, and the desperate need to believe in a miracle even when the truth is whispering otherwise. The hidden message discovery is a great turning point, and from there the book becomes a full‑on race to uncover what really happened the day Lydia vanished.

Fans of The Housemaid, Gone Girl, and The Other Daughter will feel right at home with the twists, the unreliable edges, and the way the story constantly shifts beneath your feet. It’s fast, addictive, and perfect for a one‑sitting read.

A gripping, eerie, and emotionally charged thriller that delivers exactly what psychological‑suspense fans crave.

My thanks to Rosie Walker, the publisher and netgalley for the ARC

[Julie Connor · Rating 4 out of 5]

Not My Sister was a gripping read that drew me in straight away. The pacing is good from the outset, and as the story unfolds, Rosie Walker pulls you along in a direction that feels completely natural and believable. Just when you start to feel settled, there’s a subtle sense of unease threaded through the narrative that keeps you second guessing what you think you know, making it very hard to put down.

I particularly enjoyed how the tension builds steadily throughout the book. Clues are revealed at just the right moments, encouraging you to form theories, only for the story to gently steer you elsewhere. It’s the kind of thriller that keeps your mind working alongside the plot, which made the reading experience especially engaging.

The ending was completely unexpected. The twists were clever, surprising, and genuinely satisfying. Everything came together smoothly, wrapping up the story in a way that was both impactful and well thought out.

Overall, this was an engaging, twisty thriller and a very enjoyable read. I’d happily recommend it to fans of psychological suspense who enjoy being kept on their toes right through to the final pages.

Thank you to NetGalley and the publisher for providing an advance copy in exchange for an honest review.

[Angel **Book Junkie** · Rating 3 out of 5]

Thank you to NetGalley, Rosie Walker, and Bookouture for the copy in exchange for an honest review.

This book was dark — emotionally heavy and honestly heartbreaking at times. It really pulled at my heartstrings and explored some difficult themes that stuck with me long after I finished.

That said, the first part of the book was a struggle for me. I kept waiting for things to really move forward and felt like I wasn’t getting anywhere for a while. When “Lydia” suddenly appeared, it almost felt like I had stepped into a horror story — especially considering the title — and I wasn’t sure where the story was trying to take me.

But then… around the 75% mark, everything changed. The twists and revelations completely caught me off guard and finally delivered the emotional impact I had been waiting for the entire time.

Final verdict: A slow start that required patience, but a powerful final stretch that made the journey worthwhile. Dark, emotional, and ultimately memorable — even if it took a while to get there.

[Serena · Rating 5 out of 5]

Twelve-year-old Lydia vanishes without a trace, leaving her sister Annabel and their mother Wendy shattered. Soon after, Annabel’s father walks out, and the family fractures completely. Six years later, Lydia suddenly comes home, alive, older, and with significant gaps in her memory. Wendy is overjoyed. Annabel is not. Even the family dog doesn’t recognize her. As Annabel grows increasingly convinced that this girl is not her sister, the story spirals into a tense psychological game where nothing, and no one, feels entirely reliable.

This is a slow-burn psychological thriller that rewards patience. The suspense builds gradually, tightening chapter by chapter, until it becomes genuinely head-spinning. I loved how Rosie Walker keeps the reader constantly off-balance; I went back and forth repeatedly on who was unraveling faster: Annabel, Wendy, Lydia… or possibly all three. That uncertainty is the hook, and it’s executed beautifully. I lost sleep with this one and found myself irritated when real life (rude) interfered with my reading time.

Content-wise, readers should be aware of themes involving child disappearance, family trauma, abandonment, and psychological manipulation. None are handled gratuitously, but they are central to the story. My only minor critique is that the pacing may feel a touch slow for readers who prefer nonstop action, but for me, the creeping dread was exactly what made it so effective. I think fans of Gillian Flynn and Freida McFadden will feel right at home here. This was a compulsive, unsettling, and very satisfying read, and an easy five stars.

A special thank you to Bookouture for providing this book for review consideration via NetGalley. All opinions are my own.

[Vanessa Croft · Rating 3 out of 5]

I read Not My Sister via an eARC from NetGalley.

Told from the perspectives of both the mother (Wendy) and sister (Annabel), this book explores the aftermath of a family upon the return of its missing daughter (Lydia). The writer does a good job of developing the characters and positioning their POV, however much time is spent on internal monologue which took away from the general pace of the novel. Some of Wendy's moments felt very repetitive and I found myself wishing she would just get on with it since we already had spent so much time on her emotions regarding her daughter's return.

Overall, the twist was precisely what I had expected and I found myself reading not because I wanted to find out what happened, but because I was enjoying Annabel's character arc.

Readers who like the accessible narrative style of Freida McFadden will enjoy this novel.

[Erica H · Rating 4 out of 5]

Review of advance copy received from Netgalley.

Of the books, I read this week, this was the one I most wanted to pick back up to see what happened next. Where a lot of thrillers start to sound very similar or have plot twists that ruin the whole book, the twists in this book just kept making it better. One aspect that I really liked about the book is that at first, you don't know which character you supposed to root for; it kept things interesting. I was invested and had to keep reading.

This was my first Rosie Walker book, but I just added the Bride's Secret to my TBR list. I rated this book 4.5 ★s out of 5.

[Britney Ireland · Rating 4 out of 5]

I voluntarily requested this book from NetGalley for an ARC copy in turn for my honest opinion.
Thank you NetGalley and Bookouture for the ARC read.

I enjoyed this book very much.

Imagine your sister who has been missing for 6 years shows back up on your doorstep after all that time. Your mom welcomes her home with open arms but you cant quite seem to believe that she is who she says she is.

This book has twist and turns that you wont see coming which makes it a great mystery thriller from start to finish.

Thank you again #NetGalley and Bookouture for the early read. I highly recommend.

[Tamanna · Rating 5 out of 5]

I was so hooked to the book that I forgot about time
I have read the whole book in 3 days
What a spectacular read it was!!!!
My mind is blown, I am so into the characters that I could never predict the twist , it was literally jaw dropping
The book is fast paced and makes you feel like you are the detective about what's actually happening, I was completely shocked when I read the end
I completely loved the book and it truly is a 5 star read ✨
Hoping to read more books from the author
Thank you for giving and arc of the book and trusting on me to read it. ❤️

[Lindsay · Rating 5 out of 5]

This really is one of those books which will keep you up all night but it’s a must read. We meet a family who have just had the best news a daughter who has been missing for years has turned up again and what should be a beautiful reunion is marred when the dog and her sister both realise something is wrong with this woman. How can she prove to her mother that she is not her missing sister or has trauma changed her beyond all recognition. What really happened all those years ago and is the truth darker than anyone could imagine. A great read with a brilliant ending!

[Nicole McCombs · Rating 4 out of 5]

I received an ARC from NetGalley in exchange for an honest review. All opinions are my own.

Imagine coming home and finding your missing sister of 6 years in your kitchen with your social media crazed mother. The emotions in this book go from excited to suspicious. 🤔 You know the girl who showed up is not really your missing sister, something is off.

The twists and turns of Not My Sister were very well written in my opinion. I gave this one 4 stars just because I felt some of it was repetitive, but the overall plot and twists were amazing!

[Becky Wells · Rating 5 out of 5]

What a read! I finished this book in two days as I couldn't put it down. Just when you think you know what's going on the author throws in another huge twist and has you questioning yourself. Very cleverly written with brilliant characters and a believable insight into mental health and twisted family dynamics.
I would highly recommend to anyone who likes a fast paced psychological thriller and enjoys a twist or twenty

[Shelly Turula · Rating 4 out of 5]

Dark and twisted! I had not read Rosie Walker prior to Not My Sister but I have definitely added more by this author to my TBR pile! There were parts of this book that seemed redundant, however, the story sucks you in until you reach the twisted conclusion! Highly recommend! Thanks to NetGalley and Bookouture for the ARC. All opinions are my own. Rating: 4 stars, expected publication date 04 Mar 2026.

[Kimberly · Rating 4 out of 5]

3.5 Stars

Thank you NetGalley for keeping me busy reading the latest and greatest!

Alternating points of view and timelines.

I had the gist of the story figured out pretty early on. Details were still a bit blurry until the end and once I was 80% through, I was thrown for a fun loop.

Would I read it again? Probably not.

Should you read it? Why not?

[Angelynn23 · Rating 5 out of 5]

A gripping and dark story of two sisters. It has loads of great twists that I couldn’t stop turning the page. Loved the story and enjoyed the read. Thank you NetGalley and to the publisher Bookouture for the ARC.

[Tina Fulcher · Rating 5 out of 5]

What an amazing read. Kept me gripped from start to finish. What a twist! So well written and highly recommended. I was lucky enough to receive an advance copy and leave this review willingly.

[Ryan Richards · Rating 4 out of 5]

the twists were so good!!! swear I didnt breathe for the last 20 chapters!