Dead Simple by Peter James

This is a thriller that I came across by accident but which has led me to become hooked on the author.
The plot starts with a stag night prank that goes horribly wrong, leaving the impending groom encased in a coffin.
The story introduces a police detective who is leading the hunt for the missing groom and the plot twists and turns toward an unexpected ending.
This is the sort of story where you get half way through and then suddenly it makes you think, "whoa, I wasn't expecting that". I can't say much more without giving the plot away, but Peter James has a fascinating imagination.