"Their Little Secret" is Mark Billingham's 16th Tom Thorne Novel. What I like about this series is the character development: the Tom we meet in "Sleepyhead" is not the same Tom as the one in "Good as Dead", and he's different (consistently so) from the one in "Their Little Secret". Nicola Tanner is also evolving, healing in one sense but still broken in another. All good.
The plot features interesting characters (a suburban mum with a secret, a conman), and the book ends before this reader got to know them well enough for her liking. Still, it's the usual Billingham page-turner. And Tom's a treat, as always.