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The Munsters: 1x10

Autumn Croakus

Grandpa is feeling lonely and depressed so he contacts a matrimonial agency to find a mate. The agency sends over a nice looking elderly woman who find Grandpa to be delightful. She turns out to be the Black Widow: she makes her living by marrying her suitors, getting them to sign a life insurance policy naming her as beneficiary, and then murdering them.

The Munsters: Season 1 Episode 10
Nov. 26, 1964