If you were a famed mystery playwright with a devastating string of recent flops, what would you do for a can't-miss thriller script? Beg for it? Pay for it? Kill for it? Get snared in Deathtrap, the fiendishly funny film version of Ira Levin's Broadway hit starring Michael Caine as the blocked writer, Dyan Cannon as his loving, naive wife and Christopher Reeve as a former student who's written a play so flawless "even a gifted director couldn't ruin...