The Irresponsible Reader

The Key to a Killer

by Olivia Blacke

DETAILS:
Series: Ruby and Cordelia Mysteries, #3
Publisher: Minotaur Books
Publication Date: October 20, 2026
Format: eARC
Length: 368 pg.
Read Date: October 7, 2026

What’s The Key to a Killer About?

With two solved murders under their belt, it’s time for Ruby and Cordelia to focus on one closer to home—very close to home. It’s time to talk about Cordelia’s murder.

Cordelia begins to remember more about that fatal night—which starts to point them in the right direction.

All they have to do is hope her memories continue to come back, while they’re distracted by industrial espionage, marital difficulties (obviously, not either of theirs), Cordelia’s brother, Ruby’s budding romance, workplace struggles, new ghost abilities (better said, Cordelia learning about abilities she had), a series of break-ins at their apartment building, some questionable political moves, a persistent journalist, and a few other things. Most of which could point to the solution to their puzzle. But might not.

Why did I pick this up? Why did I keep reading?

I grabbed this to read because I’d read the first two books in the series and had to find out what happened next. I’ve been curious (as Blacke wanted the reader to be) about Cordelia’s murder since her first book. It wasn’t too long before Blacke made it clear to the reader that she didn’t die accidentally or by her own hand (no matter what Cordelia’s ghost might have thought), so I just had to know whodunit.

Also, I’d read Blacke’s last 5 books, and have found her to be a completely reliable author, and I’m now predisposed to pick up something with her name on it without much thought.

I kept going because I like the characters, first and foremost, and enjoy spending time with them. Curiosity (see the opening paragraph of this section) was obviously a driving force, too. But Blacke kept putting them in interesting circumstances, things that raised more questions than they answered, and watching the two bounce around from red herring to red herring to a thing that actually matters, just not in the way they thought…Blacke got everything right this time.

What does this book tell us about humanity?

I think The Key to a Killer—like the rest of the series, actually—has two important themes about humanity. The first is trust. Extending trust to the right people, cutting off that trust when we should, and then relying on those we’ve trusted. If we act like islands (think Simon and Garfunkel’s “I Am a Rock”), we flail. Both Ruby and Cordelia are proofs for that.

The second is the need to not be alone. Ruby needs people to keep her out of her head and for safety. Cordelia needs people to care for, to help her not make self-destructive choices, to just be around. The isolation she wrapped herself in wasn’t good for her. Ruby was likely headed in a similar direction before she and her new roommate got together.

I guess really, both of those could be summed up in a need for community of some sort—the people in their building, their coworkers, fellow ghosts, family. Now, it’s clear that not everyone in the building or at work should be depended on—and ghosts can be less than reliable (just like the living)—but in actual community is where humans, living or not, thrive.

So, what did I think about The Key to a Killer?

I do think the first in the series, A New Lease on Death</b was more entertaining—the humor was a bit more pronounced, the fun of watching the two figure each other out, and so on—made for more fun. Death at the Door was a bit more tense, with more implied danger. But Blacke topped the others here with heart and intrigue—the threat of violence seemed both more pressing and less likely (I think this has to do with the number of allies that Ruby has picked up by this time). She took everything she’s done so far and kicked it up a notch or two (except maybe the humor—but that could be in an “eye of the beholder” situation this was more about earnest effort), as she should. The result is a novel that’s just a little bit more satisfying than its predecessors.

I’m assuming that this is the end of the road for this duo. I’d be very pleased to find out that I’m wrong, but it feels like this Blacke has tied up enough that she can leave them to un-recorded adventures. If that’s the case, this is a satisfying end-point for the pair. We see them in good places, with a lot tied up, some good closure on lingering questions about Cordelia’s life (beyond the question of “who killed her”)—and Ruby in a good place, too.

Obviously, learning more about Cordelia’s final days gives the reader a lot to chew on. Without wanting to give too much away, learning what we do about her married boyfriend is rather revealing—and I’m glad Blacke went the way she did with that. In the end, she’s a more complex and flawed character than she seemed to be when we first met her spectral form.

There’s one clue that took Ruby frustratingly long to figure out—and I’m less than happy with one of her subplots was left (there’s something to be explored if Blacke goes for a fourth book). But overall, the arc she’s been on is very well done. Honestly, those two points are my only complaints about this book.

I don’t know if this is the best book to jump into things with—but it would work for someone looking for a ghosty-cozyish mystery for October. I think you’d be better off with three of the books to give you a solid ghosty story from the beginning. Obviously, I think most of the audience for this will be those like me who just want the big question about Cordelia answered and who look forward to the adventures up to that reveal (which was done so nicely).

I’m looking forward to whatever Blacke has coming next, too. I think most readers of this book will be, too.

Disclaimer: I received this eARC from St. Martin’s Press via NetGalley—my thanks to both for this. This post contains my honest opinion about a book I chose to read.

This post contains an affiliate link. If you purchase from it, I will get a small commission at no additional cost to you. As always, the opinions expressed are my own.