The Key to a Killer

Ruby and Cordelia Mysteries #3

by Olivia Blacke

A woman and her ghost roommate investigate their most personal case yet in Olivia Blacke’s The Key to a Killer, the next book in the Anthony Award winning Ruby and Cordelia Mysteries.

When Ruby Young discovered that her Boston apartment was haunted, she did what any reasonable person would do: befriend the ghost. Their relationship overcame a shaky start—Cordelia Graves never wanted a roommate in life, she certainly didn’t want one in death. After working together to solve a few murders, the two are close friends, but there’s a lingering question neither of them have been able to answer: what led to Cordelia’s death?

Lately things have been adding up that suggest foul play. And when Cordelia’s memories of that day start to come back, the roommates can’t ignore it anymore: Cordelia was murdered. Ruby and Cordelia are going to have to piece together what Cordelia’s final days looked like—otherwise a killer could go free.

Genres: Mystery, Paranormal, Fiction, Cozy

368 pages, Hardcover

Expected publication October 20, 2026

About the author

Mysterious, Spooky, Cozy & Kooky

Olivia Blacke (she/her) is the Anthony Award-winning author of the paranormal Ruby and Cordelia Mysteries, as well as the cozy Record Shop Mysteries and the Brooklyn Murder Mysteries. She had her first ghost encounter when she was five, but wasn’t involved with an active crime scene until much later, when she accidentally stepped into a chalk outline on a Manhattan sidewalk. Armed with a Criminology degree, she channels her love of the supernatural and passion for writing into darkly humorous supernatural mysteries. She wants to be a unicorn when she grows up.

A NEW LEASE ON DEATH: https://bit.ly/ANLOD

Social media links, blog, and up-to-date news is found at: OliviaBlacke.com

Newsletter signup: http://www.oliviablacke.com/newsletter

Reviews

[Janet]

I can’t wait for this book!! I loved the first two!

[Megan · Rating 4 out of 5]

I picked up the first book in this series because I liked the cover. I’m so glad I did because I’ve really enjoyed this cozy, quirky, charming series. Ruby and Cordelia are such an unlikely but dynamic duo.

[Joan · Rating 5 out of 5]

Review of Uncorrected Digital Galley

Cordelia Graves hears Ruby calling for help and hurries to assist her, only to discover that Ruby is in the bathroom, the one room in the apartment that Cordelia refuses to enter. That’s the room where, six months ago, she died.

But Cordelia forces herself to cross the threshold; Ruby needs help.

Ruby Young is deathly afraid of spiders. And there’s a spider on the bathtub faucet. Cordelia scoops him up and puts him outside on the window ledge.

Cordelia hadn’t wanted a roommate when she was alive, but now she and Ruby have come to a perfect partnership between ghost and breather.

And now, Ruby stuns Cordelia when she announces that it is time to find out who killed Cordelia . . . and why.

=========

Third in the author’s Ruby and Cordelia Mystery series, the book has sufficient backstory for readers new to the series and works well as a standalone. With the expected characters in place, and the strong relationship between Ruby and Cordelia, readers will be pulled into the telling of the tale from the outset.

The haunted apartment is sure to capture the reader’s imagination as the intriguing cozy mystery plays out. Some plot twists and a few unexpected surprises will keep readers guessing as the unfolding story heads toward a denouement that may be a total shock.

Readers who enjoy cozy mysteries, stories with a paranormal slant, and captivating mysteries will find much to appreciate here.

Highly recommended.

I received a free copy of this eBook from St. Martin’s Press / Minotaur Books and NetGalley and am voluntarily leaving this review.
#TheKeytoaKiller #NetGalley

[Alicia Schaper · Rating 4 out of 5]

✨Thank you so much to NetGalley and St. Martin’s Press for the opportunity to read this ARC!✨

🔑 The Key to a Killer had me happily jumping back into the world of Ruby and Cordelia, and this series just keeps getting better! In book three, Ruby and her ghostly roommate Cordelia finally start piecing together the mystery behind what really happened to Cordelia... and I was completely along for the ride 👻🕵️‍♀️

I absolutely love a cozy mystery with a little paranormal twist, and Ruby + Cordelia’s friendship continues to be my favorite part of the series. Their relationship is funny, sweet, and full of heart. Cozy mysteries can be a little hit-or-miss for me sometimes, but this series keeps winning me over with lovable characters and mysteries that keep me hooked!

⭐️ Cozy mystery + ghostly besties + mystery-solving = such a fun read! ⭐️

⭐️3.5 stars!⭐️

[Penny · Rating 4 out of 5]

I just love this series, so was of course excited to see this new book. Cordelia and Ruby have come to really appreciate each other, and look out for each other, in this third book. Even though they have a hard time communicating because of the alive and dead situation, they make it work. When they decide to start investigating Cordelia’s murder, all kinds of information and secrets come to the fore. I just loved this book, and I’m really hoping there will be more in the series. These two, plus a few side characters, really pull at my heart strings. There were a couple of inconsistencies from the first two books, but that is easy to overlook since I enjoyed this so much. More, please. Recommend. I was provided a complimentary copy which I voluntarily reviewed.

[Michelle Treas · Rating 5 out of 5]

Thank you to Netgalley and Minotaur Books for the arc of this book. The Key to a Killer is the third book in A Ruby and Cordelia Mystery series. This book picks up shortly after the second book in the series. It is possible to read this book as a stand alone, the book gives us background that you would not be lost or confused. Ruby and Cordelia are a funny and quirky duo. Even with their communication barriers their banter is laugh out loud funny. This fun, cozy mystery was a quick light read. I recommend this book if you love a good light mystery. I cannot wait for the next book in this series.

[kindle.babe · Rating 4 out of 5]

𝗥𝗔𝗧𝗜𝗡𝗚: ★ ★ ★ ★
𝗔𝗥𝗖 𝗥𝗘𝗩𝗜𝗘𝗪:

I was so excited to see we are getting more of Ruby && Cordelia! I love this ghostly friendship and their mystery adventures. This was just as if not cozier than the first book. I don't want to give much away but if you love a good lighthearted paranormal/ghostly friendship duo who solve mysteries then this book will be for you. You will love these two and their stories as much as I do I am certain of it!

𝗧𝗥𝗢𝗣𝗘𝗦: Mystery, Cozy, Paranormal, Thriller, Friendship

Thank you NetGalley, St. Martin's Press | Minotaur Books, & Olivia Blacke for an ARC in exchange for an honest review. Releasing on October 20, 2026!

[Marissa · Rating 4 out of 5]

Kindle Copy for Review from NetGalley, St. Martin's Press and Minotaur Books.

I received a free, advance copy of this book and this is my unbiased and voluntary review.

A haunted apartment leads to owner befriending the ghost. When her roommate suddenly dies, they will end up working together once again to solve how her roommate died. Recollections are cloudy as things are not what they appear. Can they find a murder before the killer strikes again n this mystery as memories slowly return.

[Danielle D · Rating 3 out of 5]

In this latest installment of the series, we finally learn who killed Cordelia. After so much buildup, the resolution takes a direction that didn’t quite work for me, and it left me feeling a bit underwhelmed. Even so, I’m still enjoying the paranormal elements and the main characters. The ongoing mystery surrounding what’s happening at Ruby’s workplace remains compelling, and that storyline alone will keep me reading the series.

[Emily Malfitano · Rating 4 out of 5]

I loved this one! I adore cozy mysteries. I’ve gotten so attached to this series and the dynamic between the FMC and her ghost roommate. I was really happy we finally got answers surrounding Cordelia’s death, but at the same time I feel like there’s still so much more story left to tell. I’m definitely not ready to leave these characters behind yet and really hope there are more books about their adventures.

[LittleRead · Rating 4 out of 5]

I love Ruby and Cordelia. Their. relationship has grown over the three entries in this series and you have to sometimes remind yourself that one of them is no longer among the living. It sounds odd, but it works. Really well actually. There’s humor, mystery and lots of twist and turns to keep you guessing until the end. I really enjoy this series and find each entry would read fine as a stand alone, but it’s too good to not read them all.

[Jeremy Reppy · Rating 3 out of 5]

“The Key to a Killer” was a decent read. It starts off slow and plods along for a while but eventually picks up pace and improves. I still think Cordelia and Ruby should have figured out a more effective communication method, but they made it work. I liked the “new” ghost powers/abilities that Cordelia learns from Harp. I also liked that Ian learns Cordelia is a ghost and helps Ruby solve the mystery of Cordelia’s death, with the circumstances and killer being unexpected.

[Terri · Rating 2 out of 5]

I really enjoy the other novel in the series and I know I skipped one. The characters are fun and the story is too, so I really hope the author cuts down on some of the repetition that happens in each chapter. Also we should get to the action a little bit quicker because we don't need as much lead up as is there. These are fun! Cozy mysteries even if they have a little bit of a dark side to them.

[C. McKenzie · Rating 4 out of 5]

The story was familiar, and the characters were not very well-rounded; however, the humorous interactions between the ghost of Cordelia and Ruby kept me reading. While the pacing was slow at the beginning, it picked up later, and I didn't guess the killer or how they committed the crime until the end.

Overall, it's a quick, light read.

[Tiffany (areyoutellingstories) · Rating 5 out of 5]

Our favorite ghost/breather crime-fighting roommate duo is back! And they've gotten so good at communicating with one another, I'm so proud of our roomie besties! I'm so glad we finally know who killed Cordelia! I can't wait to see what our little dynamic duo gets up to next!

[Dawn Nicole · Rating 4 out of 5]

I've thoroughly enjoyed this series, and it was fun to spend time with Ruby and Cordelia once again. It got off to a slow start but came to a satisfying conclusion. If you like cozy murder mysteries, this is a fantastic series to read!

Thanks to NetGalley and St. Martin's Press for an ARC in exchange for my honest review.