During Reverend Lovejoy's sermon, Maggie is scratching. The family takes Maggie to see Dr. Hibbert, who diagnoses Maggie with chicken pox. Inspired by Flanders' suggestion of purposely exposing his sons to the chicken pox, Homer invites all the neighborhood kids over to the Simpson house for a "pox party". He ends up catching it himself, by drinking from Maggie's milk bottle, having no childhood immunity. Milhouse's parents attend the party, and after getting drunk on Marge's custom Margaritas, they resume their relationship.
Milhouse feels neglected because his parents aren't fawning over him as they did while they were separated. He schemes to break them up again, and Barthelps him with a plot borrowed from The O.C. The boys place a bra, belonging to Marge, on Kirk's bed. Luann finds the bra, assumes Marge is having an affair with Kirk, and informs Homer. When Homer confronts Marge, she angrily denies the allegation and kicks him out of the house.
In order to bring Homer and Marge back together, Bart and Milhouse plan to throw a dummy that looks like Bart off a cliff into the river below, while Homer and Marge watch. However, after breaking his glasses, Milhouse accidentally pushes the real Bart off the cliff. Homer leaps into the rapids to rescue him, but they end up clinging on to a rock near a waterfall. There Bart confess to Homer about leaving the bra in Kirk's bed, causing Homer to strangle him. Marge tells them to trust her, and let go of the rock. They let go and she catches them, swinging from a rope attached to a tree. Once safely on the river bank, Marge and Homer reconcile. They see Milhouse, thinking Bart died, jump off the cliff. The episode ends with Milhouse's fate unresolved. But they likely save him.