As Annie plans a mysterious day of cleaning as Eric discovers the shocking news that Mary ran away from "The Colonel"'s to come back home because of a devious scheme she had with Robbie and freaks out. Eric is convinced that more trouble is brewing and goes to insane lengths to find answers. In reality, Mary is heading home for a huge surprise birthday party for Eric, attended by all the people whose lives he's changed for the better in the past few years. Chores at home are interrupted, however, when Ruthie discovers Frankie and Johnny's baby, Mercy at the Camden front doorstep. Meanwhile, Lucy stays with her friend Mike's (guest-star Jeremy Lelliot) near catatonic mother for the day, and drops a proverbial bomb on Lucy. Also, Matt and Simon try to figure out why they delivered Mrs. Bink (guest-star Eileen Brennan) to the hospital.