Baby's birthday is coming up, and Earl decides the best way to Baby's heart is by buying him things. He brings him home a bat, which is promptly used on Earl's head. While Earl is unconscious, Fran decides to pack up some of Baby's old things for charity,
While rummaging through them, Charlene comes across Fran's nest. Charlene quickly notices that the name of another family in the nest, the Molehills. When thinking about the subject, Fran remembers a day at Lamas class where the was an earthquake. Her nest and Mrs. Molehill's got switched, which leads the family to think that Baby may not be theirs. While this idea excites Earl, Fran and Baby are quite dismayed. Earl decides that the only thing to do is meet with the Molehills.
The next day, Gus, Glenda, and Aubrey Molehill arrive. It's apparent from the very start that there might have actually been a baby switch. Gus acts exactly like Baby, while Aubrey is green, and well-mannered. While Gus and Earl are quick to decide that there has been a switch, Fran demands absolute proof.
So, the parents and baby's head to Absolute Proof Laboratories to have some tests run. The tests include blood screening, electroshock, submersion, and spinning very fast in a chair. Once the Doctor has checked that their credit card cleared, he announces that Aubrey is actually the Sinclair's baby, and Baby is the Molehill's.
Back at the Sinclair home, the family is trying to celebrate Aubrey's birthday. Unfortunately Aubrey isn't as great as Earl believed. He's very accident-prone, whiny, as well as being a hypochondriac. A game of peek-a-boo nearly sends him into a full-blown panic attack. Fran gets back from the store with all sorts of natural and expensive foods for Aubrey's new diet, when she realizes that her baby, Baby, is gone and goes into a frenzy.
Soon after, Glenda Molehill arrives to retrieve Aubrey and return Baby. Both sets of parents are feuding for the bay they want when Robbie interjects and tells them to act like adults. They go to see Solomon the Great.
Solomon decides the only fair way to decide who gets Baby is to cut him in half. When there is no objection, he does so in a magician's style. The Molehills, distraught at the idea of having half a baby grab Aubrey and run. Earl confesses that it wouldn't matter how many pieces Baby was in, he'd still take him home. After hearing this, Solomon restores Baby to whole, and the family is reunited. As an added bonus, Solomon makes the Doctor magically appear and say the test result was wrong and Baby is really theirs.