In the 1950s, Mary Ann Benedict participates in a genetic experiment financed by the U.S. government, which is intended to create a physically, mentally, and spiritually exemplary human. However, doctors are surprised when Mary Ann gives birth to fraternal twin boys with exceptionally different body types, and the infants are separated. The model child of the experiment, Julius Benedict is strong, intelligent, and kind-hearted, and grows up on a remote tropical island helping research scientist Professor Werner. On Julius’s thirty-fifth birthday, Werner tells Julius about his twin brother. Despite his ignorance of the outside world, Julius decides to leave the island to look for Vincent, who was raised in a Southern California orphanage. In Los Angeles, Julius finds Vincent in jail for unpaid parking tickets. Although initially surprised to discover that his brother is a small-time criminal, Julius selflessly protects Vincent from violent debt collectors and pays off his overdue fines. Vincent doubts their relationship, but takes advantage of Julius’s ardor by using him to help steal a rental car. Afterward, they meet up with Vincent’s on-again-off-again girl friend, Linda Mason, and her sister, Marnie. While Marnie disapproves of Vincent, she is immediately attracted to Julius. Over dinner, Julius tells Vincent that their mother died in childbirth, but Vincent procures documents from the orphanage claiming he was abandoned. Thrilled to learn she may still be alive, Julius finds her address and meets her former lover, Granger, one of the many sperm donors who contributed to the experiment. Granger explains that Mary Ann was told Julius died at birth, and gives him the name of Dr. Mitchell Traven in Los Alamos, New Mexico, who may know of her whereabouts. Meanwhile, Vincent finds a prototype jet fuel injector worth $5 million in the trunk of the stolen rental car, with instructions stating that it must to be delivered to Beetroot McKinley, an industrialist in Houston, Texas. Hoping to claim the money himself, Vincent packs up the car, but Julius suggests they stop to meet Dr. Traven along the way. When Linda finds out about their plan, she insists on bringing Marnie, who hopes to get closer to Julius. In Los Alamos, Dr. Traven confirms the truth about the experiment and reveals that Mary Ann now runs an artists’ colony north of Santa Fe. The scientist is not surprised by the twins’ vastly different lives, and belittles Vincent for his inferior genetic makeup. Vincent is deeply offended, but Julius reminds him that although he has suffered a difficult childhood, they will soon find their mother and become a family. As they continue their journey, Vincent teaches Julius various social cues to help him acclimate to the real world, and the brothers become close. When they stop at a motel, Vincent insists on bunking with Linda, forcing Julius and Marnie to share a room. Although Julius is nervous being alone with a woman for the first time, he willingly submits to Marnie’s seduction. At the artists’ colony, Vincent and Julius unknowingly meet their mother, who conceals her identity by claiming that Mary Ann has passed away. Crushed, Vincent drives to meet Beetroot McKinley in Houston, leaving Julius and their girl friends stranded in the desert. When Linda warns that Vincent may be in danger, Julius sends the sisters home and makes his way to Houston. Vincent drops off the fuel injector with McKinley, who makes good on his promise and gives Vincent a briefcase filled with cash. Seconds later, however, McKinley’s original deliveryman, Webster, arrives and vindictively pursues Vincent for the money. Julius interferes, and Vincent surrenders the briefcase in order to keep his brother safe. Webster intends to kill them anyway, but the twins bury him under a pile of heavy metal chains and confiscate the money. Julius insists they do the honorable thing by returning the fuel injector, and their honesty earns them a $50,000 reward, which they use to pay off Vincent’s debts and start a consulting firm. After seeing their photograph in the newspaper, Mary Ann confronts Dr. Traven for lying to her and reconnects with her sons. Sometime later, Vincent and Julius are happily married to Linda and Marnie, each raising their own sets of twin babies.