After Mac bumps into a girl named Goo when he gets something out of a tree, she thinks that Mac is her boyfriend, and Goo begins visiting Mac everyday at Foster's. With her hyper active imagination, she creates a new friend one after another, which causes a big problem for the other imaginary friends in the house. After she creates so many imaginary friends that it crowds the whole house, the others have to sleep in the Foster's bus. Can Mac stop Goo from creating so many friends?