A bank temporarily housed in a mobile home while a new building is built, looks like an easy target to break into. On the other hand, why not steal the whole bank, and rob it in a safer location.

Concert pianist Henry Orient (Peter Sellers) is trying to have an affair with a married woman, Stella Dunnworthy (Paula Prentiss), while two teenage private-school girls, Valerie Boyd (Tippy Walker) and Marian Gilbert (Merrie Spaeth), stalk him and write their fantasies about him in a diary. Orient’s paranoia leads him to believe that the two girls, who seem to pop up everywhere he goes, are spies sent by the husband of his would-be mistress. When Val’s mother, Isabel Boyd (Angela Lansbury), finds their diary, she suspects that Henry has acted inappropriately with her daughter. She contacts Orient and they end up having an affair. Val finds out about it, as does her dad.