As the class prepares to go on a school trip to the museum, Arthur has trouble going to the bathroom while other people are in there. Just before the class boards the bus, Mr Besser introduces Johan, an exchange student who will be going on the trip with Miss Graves' class and Nancy is picked to be his chaperone. The kids prepare to board the bus just as the class chaperone, Jessie's mother, arrives and immediately begins humiliating Jessie with various stories and photographs of him. When the group arrives at the museum, Jessie and Vinnie find themselves trying to escape Mrs McCoy who is desperate to pair up with them and Arthur, still in need of a bathroom, ends up partnered with Freddie. As Arthur searches for an empty bathroom, Freddie finds that he has also become kidney shy and the two desperately seek an empty rest room without success until Miss Graves recommends they visit the fourth floor exhibit on ancient napkins, the only place in the museum with an empty bathroom. Meanwhi