"Lost Our Lisa" is the twenty-fourth episode of Season 9.
After hastily boarding the wrong bus to a limited engagement museum exhibit, Lisa finds herself lost in unfamiliar parts of Springfield. Meanwhile, Bart adheres novelty items to his face, only to later discover that the glue he was given—by Homer—is permanent.
Bart and Milhouse are at a joke shop on a day off from school. After looking around, Bart buys some novelty face items and takes some glue from Homer at the Power Plant. Marge agrees to take Lisa to the Springsonian Museum so she can see the Orb of Isis, but she learns that she has to take Bart to a doctor instead, since he has the glued items stuck to his face. Since this is Lisa's last chance to see a certain exhibit, she phones Homer to ask him if she can take the bus, despite her young age. He seems uncertain, which prompts her to trick him and he unwisely agrees.
Lisa takes Bus Route 22 which passes Crackton. Having not passed the museum for so long, she asks the driver if the bus is Route 22 and learns that she is riding Bus Route 22A, the wrong bus and has to get off at the last stop, which is in the middle of nowhere. After a conversation with Carl and Lenny during his lunch break, Homer learns the error of his judgment, and rushes to find Lisa. He heads to the museum and ends up in Springfield's Russian district. He is unable to locate her amongst the crowds and bribes a workman with balloons so that he can use the workman's cherry picker to get up high. He spots her and she spots him, but the vehicle's wheels creak backwards and it hurtles down the hill. After scraping his head under a tunnel and smashing into some traffic lights, it slides off the edge of a pier at the harbor, but fortunately, the cherrypicker's "neck" is tall enough to keep Homer just above the water level. His head is caught between the two closing halves of the raised bridge but he miraculously survives with nothing more that a few tire marks across his forehead.
Meanwhile, Bart's novelties get removed by Dr. Hibbert with "terror sweat." Marge and Bart return home, thinking Lisa is crying in her bedroom. Marge asks him to apologize to her, much to the anger of Bart. Bart hears no sound or response from Lisa. With Homer and Lisa reunited, he tells her that it is all right to take a few risks in life. Thus, the two agree to go to the museum after all, by illegally entering since it is now closed. While there, the two make a fascinating discovery that the Orb of Isis is a music box which had apparently been overlooked by scientists and museum staff, and Lisa concludes that what her father said about risks was right—until the alarm goes off and guard dogs chase them out of the building.