Earl and Fran's marriage license expires. When Earl bungles the renewal test by displaying complete ignorance of the details of his marriage, Fran considers not picking up Earl's option. Earl is forced to move in with Roy, while the Sinclair's new next door neighbor, Monica – an Apatosaurus and the first divorced female in history – shows Fran that the single life has possibilities.

Planning for Baby's first birthday, the Sinclairs discover evidence that their baby may have been switched with another baby while still an egg. Earl is tantalized by the notion that there is a polite, well-behaved baby out there somewhere who might be his son. Fran is unwilling even to consider the possibility until she meets the other baby – who looks exactly like the Sinclair baby except he is green like Earl – and the other father shares certain personality traits with the Sinclair's baby.