Rx Murder (1958)

An American doctor, Jethro Jones, comes into a quiet British seaside community and becomes entangled in a murder mystery when the town gossips inform him that all of the three wives of the town doctor, Doctor Dysert (or Doctor Deadcert as they call him) have had mysterious deaths. And now Doctor Dysert is treating his own secretary, Kitty, who he wants to make her his next wife, as she has inexplicably fallen ill.