Bloo decides to open the one door at the retirement home for imaginary friends that is never, ever to be opened, and the house becomes infested with something bad.
It's "Adopt-a-Thought Saturday," when imaginary friends can be taken by new families. Mac and Bloo worry that they'll lose all their pals, and take drastic measures to make sure they don't.
While taking out the trash, Eduardo finds a puppy and decides to keep it, despite dogs being forbidden in the house due to Mr. Herriman's fear of them.