This is a long shot but I have spent hours trying to track down the title/author of a book I read a few years ago. It was a crime/thriller and I usually read well-known crime fiction authors and it was a traditionally published paperback. The plot involves a scene where a female police detective attends a meeting of swingers in a car park or possibly a dogging location. After the swingers party has finished she is snatched and held hostage. The main plot revolves around the police attempts to find her. The protagonist is, I think, a detective. I think it was one book in a series. I thought it was Peter James but I have checked the blurb on all his books and nothing fits. I will check out any suggestions so don't worry if you are not sure just fire away.
