When elderly physician Henry Willis (Sam Jaffe) refuses to finance a return to the spotlight for his wife, aging former movie star Grace Wheeler (Janet Leigh) kills him in his sleep, passing it off as a suicide.
This is one of the only three episodes in which the perpetrator is not arrested (the others being "It's All In The Game" and "No Time To Die"), as Ned Diamond (John Payne), Wheeler's longtime song and dance partner who has always loved Grace, falsely confesses to save her after Columbo informs him she is suffering from a degenerative brain disease (the primary reason her husband refused to finance her return as the physical strain of acting would have killed her) and likely no longer even remembers the murder.
Columbo's normal instincts thwarted, he makes several half turns – as though to enter the screening room – where Grace, lost in the past, is watching the film, having already forgotten Diamond's confession.
Hassan Salah (Héctor Elizondo), chief diplomat of the Legation of Suari, an Arab nation with a new young king, has a scheme for shifting power within his government.
He enlists Rachman Habib (Sal Mineo), a naïve idealist in the Legation, to help him stage the murder of a security officer, then plants evidence to make it look like the work of radicals.
He is also being blackmailed by his insatiably greedy employer, impresario Jesse Jerome (Nehemiah Persoff), over the fact that he is actually Sergeant Stefan Mueller, a former Nazi SS prison guard.
Mueller tires of the arrangement and Jerome's demand for more money, and kills his blackmailer in the middle of his famed water tank escape act, giving himself what he believes to be an airtight alibi.
The carbon ribbon has a clear imprint of everything written with it, so it is in effect a copy of the letter Jerome was typing to send to federal authorities, which revealed the motive for the murder.
Commodore Otis Swanson (John Dehner) is a retired naval officer who owns a shipbuilding company, and is not happy with the shady dealings of his son-in-law Charles Clay (Robert Vaughn), who has turned the modest and upstanding business into a name-brand production line for status-seekers.
Nor is he pleased with any of the people closest to him - his alcoholic daughter Joanna Clay (Diane Baker), his middle-aged playboy nephew Swanny Swanson (Fred Draper), his lawyer Jonathan Kittering (Wilfrid Hyde-White), and his shipyard manager Wayne Taylor (Joshua Bryant).
Final clue/twist: When Columbo holds what he says is Commodore Swanson's pocket watch to every suspect's ear, only Swanny disputes it, saying "'Tisn't" when he hears it ticking.