In Day Tripper, they encounter an alien that is a beautiful lady and they fall in lover with her. They accept her invitation to board her ship and take a ride. When they land on a mysterious planet 23 billion miles away, she then tells them that she is abandoning them, and that she has "saved the universe from the Beatles" and that her dad will be so pleased. The Beatles then say, "How could someone as beautiful as you be so mean"?! She then sheds her disguise and reveals that she is a monster alien and they then see that they were given one way tickets.
They start playing their song and the local aliens come out to listen. They soon begin to enjoy the Beatles, which turns them into wide-eyed human clones.
The Beatles then turn into aliens, for a second. Then the alien-now-humans put them into a geometric time/space traveling device and they warp back home... but as aliens. They then quickly morph back into their old Beatles selves.
Youtube link: http://www.youtube.com/watch?v=Dh4D2ngrnC8