After a music festival, four friends witness a woman being assaulted but don't intervene to help her. Later her body is found in the Thames. But only one of the group, Cassie, seems to have any lingering guilt over their lack of assistance. And it soon becomes apparent that the woman in trouble may not have been a stranger to them after all.
Alternating between the night of the music festival and a group weekend away, this is an engrossing read that slowly reveals the reason all four individuals failed in their civic duty to help someone in distress. Throw in some missing money, a toxic friendship and some sinister mishaps, and you end up with a cleverly plotted novel that will keep you guessing to the end.