Mom and Dad are ready to go out for the evening, but Arthur and D.W. are worried that their surprise babysitter might be a pirate, robot, or even Mr. Ratburn.
Arthur and his friends face a number of dilemmas trying to get ready for school in the morning, and Arthur is both hindered and helped by his little sister.
Arthur tries valiantly to save his sister from being disappointed when Mary Moo Cow, slated to entertain at D.W.'s birthday party, cancels at the last minute.
After seeing a UFO Buster has a hard time convincing his friends of what he saw, and when he gets pictures of the flying saucer, Brain comes up with an explanation for each one.