The portrait of Arthur Kendall was done by Thomas J. Wright, who also did the paintings for Night Gallery (1969).
While touching his upper lip, Sykes asks McMillan if he had gotten a haircut. McMillan says, "yes," impatiently and moves on. This is referencing the fact that Rock Hudson had shaved off the mustache he wore throughout the first season.
The stock footage of the Golden Gate Bridge is the same used in the credits of The Streets of San Francisco (1972).
Harry Hasting's castle reappears in the season three episode Death of a Monster... Birth of a Legend (1973), as McMillan Castle in Scotland.
Almost all of the houses seen in the episode are reused from Columbo (1971) and Night Gallery (1969) episodes, and several of the "supernatural" props are from Night Gallery as well. For instance: the Kendall mansion appeared in Short Fuse (1972) (as Ida Lupino's home), and the beach house was in She'll Be Company for You (1972) (as Leonard Nimoy's home); the "walking hands" and the corridor they're in had both been used in The Return of the Sorcerer (1972).