In his second solo starring film after breaking with Dean Martin, Jerry Lewis plays cartoonist George Baker's classic GI misfit The Sad Sack. Lewis' constitutional inability to do anything right brings him under the scrutiny of gorgeous Army psychiatrist Phyllis Kirk. She discovers that Lewis possesses a photographic memory, making him valuable enough to be transferred to a top secret assignment in Morocco. Assigned along with buddies David Wayne and Joe Mantell to guard a new weapon, Lewis deviates from his task when he falls in love with sexy nightclub performer Lilliane Montevecchi. She spurns him, so the heartbroken Lewis deserts the army and joins the Foreign Legion. When enemy spy Peter Lorre discovers that Lewis has memorized the assembly instructions for the secret weapon, he and his minions kidnap Lewis, Wayne and Mantell. With the help of Montevecchi, Lewis thwarts the baddies and becomes a hero--but within minutes, he's fouled up again, so it's back to permanent KP duty. Jerry Lewis still needed a straight-man foil at the time of The Sad Sack so Paramount provided him with David Wayne and Joe Mantell. By the time Geisha Boy rolled around in 1958, Lewis was finally able to carry a picture by himself.