Final clue/twist: Columbo eventually solves the case by piecing together clues left by Galvin as he suffocated in the safe.
When one of them, Vittorio Rossi (Michael V. Gazzo), decides to no longer pay and expose Gerard, the critic kills him with a bottle of wine poisoned with fugu.
Final clue/twist: Columbo figures out that Gerard poisoned the wine via the needle of the bottle opener, not in the pressure cartridge itself.
West Coast television production boss Mark McAndrews (Laurence Luckinbill) is promoted to a high-level position in New York.
He fails to name as his replacement the logical successor, TV programmer Kay Freestone (Trish Van Devere), because she is also his lover.
Freestone sneaks up to McAndrews's office and shoots him, then returns, hiding the gun above the ceiling panels of an elevator, to make the reel change successfully before the projectionist gets back.
It was once held that Van Devere's husband, actor George C. Scott, has an uncredited cameo as a television technician, but that claim has been debunked.
Columbo reveals that the actual gun had been discovered by the police some time before, and an imitation was put where she would see it, to find out what she would do.
Ed Begley Jr. has a minor role as an animal control officer and Tricia O'Neil plays a dog trainer.
He raises money in Los Angeles for his radical cause through a charity ostensibly meant to help victims of terrorism.
Because every diamond has a unique cutting habit, Devlin's ring, which he uses to mark his bottles, is proof of his presence at the crime scene.