Single, swinging lawyer David Sloane (Dean Martin) tries to circumvent his friend Harry's extramarital affair by romancing his secretary, Carol. However, David has seduced the wrong woman; Harry has actually been fooling around with Muriel. When David tells Harry that he's stolen his mistress, Harry isn't sure what's going on, but the message has the intended effect, and Harry patches things up with his wife Mary. But when Carol and Muriel compare notes, they decide that something is fishy, and the two draw up a series of demands. Muriel insists that Harry leave Mary and marry her, while Carol wants David to make it legal with her.