I knew that Honor Blackman appeared in an episode of Columbo.. but I didnt think that Patrick Macnee did.. until I saw it last week! Sadly he's not the murdering star of the show, but he gets special guest star status as the ship's Captain. The episode is called 'Troubled Waters' with Columbo's wife having won them a holiday on a cruise ship. The mudering star in this one is Robert.. er.. the fellow from Man From UNCLE!
That episode with Honor Blackman is one of my favorite Columbo episodes, Dagger of mind, from the second season.
It's the one with Columbo in London assisting Chief Superintendent Durk at Scotland Yard. Honor plays actress Lilian Stanhope, who kills a theatre producer.