Once again, Darrin has upset his mother-in-law and she is determined to make him pay for it. Literally. Extremely annoyed, she puts a spell on him that turns him into a high stakes gambler. His method of losing his money turns out to be horse racing and he persuades several others, including Larry Tate, to bet on a horse that has absolutely no chance of winning.
Samantha is not going to stand by and let everyone lose their shirt, so she pops to the stables before the race and has a little chat to the horse, giving him a pep talk. Much to Endora's disgust, it works, and the horse romps home.
A really good performance by Dick Sargent in this episode which saved it from being rather mundane, save for the typically excellent work of Agnes Moorehead as Endora.