One of the earlier Tom Thorne books - if you're new to the series, start from the beginning as although each is a standalone investigation, there is an element of continuity and this story references previous ones quite frequently. Tom Thorne is reluctantly transferred to work on a kidnap case, which turns out to have surprisingly links to a murder case that his department were working on several months ago, and turns out to be a lot more complicated than anyone expected. It's not my favourite of the series but it was a good read.