The Last of Sheila - a smart, funny, well thought mystery/thriller penned by Anthony Perkins and Steven Sondheim and with a top cast (James Mason, James Coburn, Ian McShane, Dyan Cannon). Plot is that millionaire movie producerJames Coburn's wife Shelia was killed in a hit and run accident, a year later he brings together his friends (who may or may not be involved in the hit and run) on his yacht for a series of games where people's secret's will be revealed. Only some sister turns start to take place.
Considering the cast and the writers I'm surprised this is not better know. The major flaw it does have is it's very disturbing view of the secrets we have a shoplifter, a homosexual, an ex-con and a child molester! To any modern audience one of those things is definitely not like the others. But apart from that (big) flaw this is a clever film and well worth watching.