The Spaceman and King Arthur is the story of Tom Trimble (Dennis Dugan), an engineer who has been send to the space accidentally. He is travelling in a new space shuttle. It flies through the magnetic fields, and when it starts working, a lot of situations begins. As consequence, Tom came back to the Middle Age in times of King Arthur. Despite of this hard situation, Tom stars a relationship with Alisande (Sheila White), but He finds enemies too: Sir Mordred (Jim Dale). This knight pretends to beat King Arthur (Kenneth More).