A couple's marriage is nearly destroyed by their attempts to save it in this farcical comedy. Dan and Valerie Edwards (Frank Sinatra and Deborah Kerr) are a couple who have been married for close to 20 years. Dan, a busy but successful advertising executive, believes they have a happy relationship, but Valerie feels stifled and thinks her once fun-loving husband has become a bore. Valerie consults a lawyer, Shad Nathan (John McGiver), about a divorce, but Nathan suggests she give things one more try, and recommends a romantic second honeymoon to put the spark back in their relationship. Following his advice, Valerie books a vacation in Mexico; Dan agrees to join her, but once they arrive south of the border, they encounter Miguel Santos (Cesar Romero), an overzealous shyster lawyer who grants them a divorce before they're entirely aware of what's happening. Dan and Valerie take the matter in stride and decide to use it as an opportunity to renew their vows, but just prior to their ceremony, Dan is called away on business. Dan asks his best friend, Ernie Brewer (Dean Martin), a devil-may-care ladies' man, to keep Valerie company until he gets back; however, as Ernie tries to explain to Valerie and Miguel that the wedding is off, he finds he's just become Valerie's new husband. Valerie, angry at Dan's sudden disappearance, decides not to divorce Ernie right away, while Ernie, who has long been infatuated with Valerie, is torn between his feelings for her and his loyalty to Dan. Marriage on the Rocks also features guest appearances by Nancy Sinatra and Trini Lopez; keep an eye peeled for DeForest Kelley in a bit part.