sleuth (1972, joseph mankiewicz)
A man who loves games and theater invites his wife's lover to meet him, setting up a battle of wits with potentially deadly results.
Watching the original film by Anthony Shaffer with Larry Olivier and Michael Caine. Caine redid it with Jude Law in '07, a Harold Pinter treatment and Kenneth Branagh direction.
This watchable copy is the only free version I could find on the net. Classic, though.