Libidinous Hogan (Jack Lemmon) is a landlord who prefers to rent his rooms to attractive single females. Hogan is instantly smitten with a pretty new tenant named Robin (Carol Lynley), but realizes that he'll have to contend with Robin's boyfriend, David (Dean Jones), if he's to attain the object of his desire. He gets his opportunity when he learns that the couple's living arrangement is a pre-marital experiment to see if they would be compatible as partners when sex is out of the equation.