When 8-yr-old Mac is forced to give up his Imaginary Friend Bloo, they find Foster's Home for Imaginary Friends, an amazing house for unwanted Imaginary Friends.
After a conflict with his brother, Mac is forced to give up his imaginary friend Bloo by his mom. Unwilling to be separated from one another, Bloo discovers Foster's Home for Imaginary friends, a home for imaginary friends. Initially excited Bloo proposes to stay at Foster's instead. However, they discover that there's is a catch; Foster's is a foster home and all friends there are up for adoption.