Just when you think you might know what to expect from Mark Billingham, he throws you a curve ball and maybe a kitchen sink to boot. Billingham has been writing his Detective Inspector Tom Thorne novels for close to two decades now (though it does not seem anywhere near that long), and THEIR LITTLE SECRET, the 16th in the series, takes Thorne and the reader into uncharted (but very entertaining) territory.

This latest entry is complex. It begins with Thorne being called to the scene of a suicide where a woman named Philippa Goodwin has jumped in front of a commuter train. There is no crime to investigate. It is quite clear from security camera footage that she jumped and was not pushed. However, Thorne (who is no stranger to depression and its resultant actions) is haunted by the video and takes the time to investigate the woman’s motive. He learns from her family that she recently had been romantically involved with a man who had taken all of her money and “ghosted” her --- disappeared --- without a trace.

"Billingham does an exquisite job of keeping readers guessing while giving them more information than Thorne and DI Nicola Turner possess at any given point until (almost) the end of the book."

Thorne begins looking for cases where women have been bilked in a similar fashion. But it’s a bit of an uphill slog, at least at first, particularly since other, more significant cases come calling, including the murder of a young man who gets his skull bashed in after a night of partying.

Meanwhile, Billingham gives us a series of intriguing vignettes involving the single mother of a schoolchild who struggles to fit in with the other, married moms. The situation is fairly common, but he infuses these interactions with a touch of vague unease, a sensation that increases when the mother in question has a chance encounter with an intriguing stranger in a coffee shop. Their relationship begins to blossom as they learn they have a great deal in common. While they are not a perfectly matched pair --- and who is? --- one is exactly who the other is looking for. Maybe. Surprises abound.

Billingham does an exquisite job of keeping readers guessing while giving them more information than Thorne and DI Nicola Turner possess at any given point until (almost) the end of the book. Since this is a Thorne novel, Thorne has his own set of emotional and domestic baggage to deal with, including the end of a relationship and the potential beginning of a new one. Phil Hendricks, his best friend, is around to keep Thorne (and the proceedings) from becoming too maudlin, even as his darts occasionally approach the bullseye too often for comfort. Matters --- all of them --- are not entirely resolved by the end, which makes an unsettling story all the more chilling. I don’t look for a resolution in future installments, but one never knows.

If you aren’t familiar with the author or his protagonist, or if you have been away from the series for a bit, THEIR LITTLE SECRET is a terrific place to jump on the Billingham bandwagon. The mysteries here are straightforward and ultimately link up without fuss or strain, but with enough room to insert plenty of twists and turns, particularly in the final fourth of the book. You may see some of them coming, but by no means all of them.