The Orderly World of Mr. Appleby (S02E15)

Arthur Appleby is something of a Bluebeard. He has killed his previous wives and used the insurance money to open a succession of antique shops, each one in a new town. When he meets Martha he marks her down as his next victim. However, she is not stupid and tells him that if anything untoward happens to her she has left instructions that Appleby is to be dealt with. (Prime Video)