Review: What the Devil Knows (Sebastian St. Cyr #16) by C. S. Harris

I absolutely love Sebastian St Cyr. I read the entire series last year in one long binge read. I adore the books and even if some of them have fallen into a bit of a formula, I still enjoy the characters so much. This one was high up on my TBR pile. I always set aside time in the early spring to read a new Sebastian mystery and I am never sorry about that.

The mysteries are intelligent, a little on the gritty side, and full of questionable characters all with their own motives. Going into this one, I was fully ready for just that and I wasn’t disappointed! But now that we are into book sixteen in the series, I am sure readers can’t help but wonder at what point will this series end? For me, I hope the answer is never but I also know that at some point all good things come to an end.

But until that day comes I am going to keep devouring the Sebastian mysteries and keep returning to my favorite characters. Some books in this series are able to be read as standalones and I think this one here could easily be read as a standalone if you want to check out the series but also don’t want to go back and read all the books to enjoy it!


Sebastian St. Cyr thought a notorious serial killer had been brought to justice until a shocking series of gruesome new murders stuns the city in this thrilling historical mystery from the USA Today bestselling author of Who Speaks for the Damned.

It’s October 1814. The war with France is finally over and Europe’s diplomats are convening in Vienna for a conference that will put their world back together. With peace finally at hand, London suddenly finds itself in the grip of a series of heinous murders eerily similar to the Ratcliffe Highway murders of three years before.

In 1811, two entire families were viciously murdered in their homes. A suspect–a young seaman named John Williams–was arrested. But before he could be brought to trial, Williams hanged himself in his cell. The murders ceased, and London slowly began to breathe easier. But when the lead investigator, Sir Edwin Pym, is killed in the same brutal way three years later and others possibly connected to the original case meet violent ends, the city is paralyzed with terror once more.

Was the wrong man arrested for the murders? Bow Street magistrate Sir Henry Lovejoy turns to his friend Sebastian St. Cyr, Viscount Devlin, for assistance. Pym’s colleagues are convinced his manner of death is a coincidence, but Sebastian has his doubts. The more he looks into the three-year-old murders, the more certain he becomes that the hapless John Williams was not the real killer. Which begs the question–who was and why are they dead set on killing again? (summary from Goodreads)


This book explores the underbelly world of London’s brewing industry. I was very interested in that bit of the story and I was a little let down that it wasn’t explained more in this book. The concept of a corrupt brewing industry and licenses was explained well enough but I would have liked to have seen the author expand on it more and shown readers from of the nuances of the industry itself. This was a minor thing for me though. It wasn’t a make or break in the story but I had hoped to have become more familiar with the industry more as it was part of the core of the mystery itself.

I was also sad that we didn’t get more Hero in this book. She seemed to take a backseat to the mystery itself, as did Sebastian’s character and his ever contentious relationship with this own father as well as Lord Jarvis. I still feel like the author is setting readers up for a large scale conclusion to the series that will likely spread over a couple of books. That will likely involve Sebastian, his mother, his father, and Lord Jarvis and the new Lady Jarvis. In the meantime, I think the author is getting all those pieces in place while we the readers continue to enjoy the adventures and gritty mysteries of Sebastian as we do in this book.

This mystery was (as expected) twisty with many people with motives. I love trying to click the pieces into place before Sebastian solves them. But as always, I never seem to solve the mystery or the motives. I love how Sebastian’s mind works and how he puts everything together. As a character he is brash, bold, confident, and intelligent. I just love his character so much and am so excited to see where his story goes from here.

I do wish we had more Hero in this book because she matches Sebastian for wit, intelligence, and boldness. I love her character and can’t wait to see more of her in future book! If you love historical mysteries this book series is no doubt on your radar. It’s smart, gritty, complex, and well developed! I love this series and this book was an great installment!

Book Info and Rating

Format336 pages Kindle

Published April 6, 2021 by Berkley Books

ISBN9780593102664 (ISBN10: 0593102665)

Free review copy provided by publisher, in exchange for an honest review. All opinions are my own and in no way influenced.

Rating: 4 stars

Genre: historical fiction, mystery, detective novel


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