The products of a genetic experiment, fraternal twins Julius (Arnold Schwarzenegger) and Vincent (Danny DeVito) are separated at birth. Their mother, Mary Ann (Bonnie Bartlett), is told they're dead. Now Vincent, an unscrupulous street hustler, ekes out a living in Los Angeles. Julius, raised by a scientist (Tony Jay), grows up humble, intelligent and strong, but very naive about the larger world. When Julius learns of his mother and brother, he heads to Los Angeles to find his family.