Mrs. Brown uses a Martian chemical without Uncle Martins knowledge, she then becomes irresistible to all men, Uncle Martin as well. Martin then plans to take her on a jaunt in his spaceship.

Uncle Martin is using a time machine hoping to avert the accident that caused him to land on Earth. Tim messes the machine up and lands them both in 1215 England where they accidentally intercept the Magna Carta on it's way to King John.