During a teacher's conference day, Bart and Milhouse decide to take a trip to the Springfield joke shop. Inside, Bart purchases a selection of amusing face jokes, but is disappointed to find that they won't stay on and fall off all the time. He goes to the Nuclear Power Plant and Homer suggests some super-strength glue.
Meanwhile, back at the Simpson household, Marge, Lisa and Maggie are getting ready to go to see an Egyptian treasure collection (including the "Orb of Isis") at the downtown museum. Upon leaving, Bart returns home and shocks Marge with his newly-attached facial jokes. She panics and apologises to Lisa, saying that she must take Bart to the emergency room. Lisa asks if she may take the bus alone to the museum, but Marge refuses to let her, deeming it unsafe.
Eager to see the Isis exhibit, Lisa calls Homer at work and tricks him into allowing her to take the bus. She eventually finds herself alone and lost in downtown Springfield, and after Lenny and Carl prompt Homer to go and find her, he panics and sets off to search. Dr. Hibbet helps Bart remove his facial jokes in an unusual way at the hospital, using the powers of "terror sweat".
Homer eventually spots Lisa from a cherry picker, but the brakes of the vehicle are suddenly let loose and it zooms down a steep hill. Lisa manages to save Homer, and she apologises for taking a stupid risk. He informs her of the importance of taking "stupid risks" and explains that his whole life is based upon such things. Lisa tells of her disappointment at not being able to see the Isis exhibit on its final day, and Homer suggests they take another stupid risk.
With Homer leading the way, he and Lisa sneak into the museum and look at the mystical Orb of Isis. Lisa tells of the fact that nobody has uncovered its secrets, and Homer vows to do so, accidently tripping on the velvet rail and knocking the Orb to the floor. It opens up and shows itself to be a music box. It plays a beautiful melody as Homer and Lisa lie and watch.
They close it up and return it, happy in the knowledge that they may be the only ones to ever hear the music again. Homer poignantly states that it will live on in their memories as they exit, and instead hums "the old spice song", having apparently forgotten the music they just heard.
Lisa agrees that it, too, is a good song, and the pair are chased from the museum as the alarm sounds by a pack of guard dogs.