Baywatch (1989)

S9E22 Castles in the Sand

Alex's weekend takes a chaotic turn when she sets out to find the creator of intricate sand castles that mysteriously appear on the beach each day. Meanwhile, she’s left to keep her childhood friend Sam's fiancée, Diana, entertained. Things get complicated when Diana develops a crush on Mitch, leading him to ask Alex to pretend to be his girlfriend to distract Diana from him.