Nothing makes you more aware of the passing of time than picking up the latest book in a mystery series that you've loved from the beginning --- and then realizing it’s the 19th installment. That's what happened to me when I got my hands on A KILLING OF INNOCENTS, the new entry in Deborah Crombie's stellar police procedural series starring married detectives Duncan Kincaid and Gemma James, who have been working together since the first volume premiered almost 30(!) years ago.

"[Crombie's] secondary characters, in particular, continue to grow in depth and interest, with intriguing plot directions of their own."

Three decades might have passed in our world, but fortunately, time doesn't seem to work quite the same way in Duncan and Gemma's London. Sure, they are both a bit older than they once were, and their little family has grown and started to grow up. Gemma's son, Toby, is rehearsing for his first big ballet role in The Nutcracker, while Duncan's son Kit, who enjoys cooking, is beginning to explore career options. The balance between the domestic and the professional is something that Crombie has always excelled at, and that's on stellar display here.

Toby's impending debut is quickly overshadowed by a case that pulls in both his mum and stepdad. Gemma and her longtime colleague, Melody, have been assigned to a task force studying a recent rise in knife crimes in London. On the surface, it should be more of a desk job assignment. But when Duncan and his colleague, Doug, stumble onto a perplexing case --- a young medical student killed, skillfully and quickly, by a sharp implement in Russell Square Park on her way home from the hospital --- Gemma's assignment (not to mention her innate curiosity) drags her into the investigation as well.

The victim, Sasha, appears to have had no enemies or rivals; she doesn't even seem to have been involved with anyone romantically. Her brother, on the other hand, has gotten mixed up in some very shady business. Might Sasha have been a casualty of a dispute with her brother? Or could her death have been meant as a warning to him? Duncan, Gemma and their colleagues question Sasha's roommate, family and colleagues. Gemma and Jasmine Sidana, the delightfully prickly detective inspector, even go undercover at a high-end club in a particularly juicy scene. But the team's leads don't seem to link up. And then there's another in a spate of knife deaths.

I often advise readers that they easily can pick up a later novel in a series without worrying about missing anything. That's not entirely the case here. Sure, the mystery itself would be absorbing regardless of your knowledge of the players involved. However, at this point the number of supporting characters is so extensive and their complex backstories so interwoven that Crombie relies on her readers for a certain degree of familiarity. The good news is that these secondary characters, in particular, continue to grow in depth and interest, with intriguing plot directions of their own.

I, for one, will definitely be picking up book #20 featuring these characters who have grown so familiar yet remain fresh and interesting.