What happens when children outgrow their imaginary friends? They take them to Madame Foster's Home for Imaginary Friends, a vast Victorian mansion with endless rooms and hundreds of thought-up playmates. At the heart of the story is Blooregard (aka Bloo), an imaginary friend created by an eight-year-old boy named Mac. Although he's usually shy, Mac feels confident when Bloo's around. Bloo, on the other hand, is bold and self-assured, and often gets himself into a mess by acting before he thinks. Follow the adventures of Mac and Bloo in a world where imaginary friends actually come to life. Nothing is ever mundane when you hang out at "Foster's Home for Imaginary Friends"!
A toy box appears at the front door of Foster's and Frankie is ordered to take it to the attic. When she looks inside the box, she gets sent to a strange world which has an imaginary friend that does whatever she wants. Frankie decides to stay because she never gets any appreciation for all her hard work. Bloo, Mac, Wilt, Eduardo, and Coco set out to rescue her.