When a large and dangerous imaginary friend is destroying the city, Imaginary Man comes and saves the day, and now, Mac is a fan. But once Mac is his sidekick, Bloo is jealous and joins forces with Nemesis, Imaginary Man's mortal enemy. Will justice or evil win in the battle of the superfriends?

The residents prepare for the annual house photo. Meanwhile, Bloo and Mac search for an answer behind a weird photo of Foster's taken years ago, Eduardo gets an "extreme makeover" from Duchess that surprises the other residents, Coco realizes she needs to lose weight and Wilt has trouble being in the house photo without getting his head cut out from the banner.

When the friends go out to the beach and leave Bloo in the house alone on purpose so that he doesn't ruin the fun, he and Mac try to squeeze in as much fun as possible and make it the best day of their lives, but are they bringing the house down?

Old Man Rivers, who lives across the street from Foster's hates imaginary friends, and on "Adopt-A-Thought Saturday", his grandson, Young Man Rivers, torments Bloo. Meanwhile, Bloo and Madame Foster throw papers - that are adoption forms - at Old Man Rivers, who keeps them for himself. What will happen?

Bloo and the gang arrive at Mac's house for slumber party that Mac didn't plan to have on a school night. But because they are all so loud, Mac's Mom could wake up and get them all into trouble. Will the slumber party be a success or a failure?

Bloo, along with the rest of the Imaginary Friends (besides Edwardo) and Frankie, plan a surprise party for Mac. However, Mac wants no part of it.

Bloo notices after a trip to the grocery store that Frankie has left the keys in the bus, and decides to take Mac for a joyride in the Foster's bus, and Wilt promises to keep it a secret. Both Bloo and Mac get lost, and now Wilt has ke keep it a secret from Frankie while telling off Eduardo (who wants to buy a mattress at half off), Coco (who feigns illness) and Mr. Herriman as well as Goo, who creates a Mr. Herriman who speaks jibberish, a Mac look-alike with a spotted tongue and a Japanese-speaking Blooregard. When Frankie get suspicious about the missing bus, can Wilt keep his secret safe?

Foster's is being put on TV, and Frankie wants everything perfect. Meanwhile, Cheese keeps appearing at Foster's, even after being told numerous times that he doesn't live there. So, in an attempt to keep him out, Mr. Herriman installs a security system. Unfortunetly, due to misreading the directions, nobody knows the password except for Cheese, who saw Herriman input the code. But everything the gang tries to get the password out of Cheese fails, and the news crew is only around the corner. Can the gang succeed and get the password out of Cheese?

Bloo announces that a one-eyed cat-like imaginary friend is in trouble. No one wants to help him at first because it might be a trick, but Madame Foster forces Frankie, Coco, Wilt, and Eduardo to help him. They find that the imaginary friend is stuck in a tree and Bloo tries to help by climbing on top of them. Instead of helping, they fall and Frankie yells at Bloo. Madame Foster pitches in and using a large brown stick, she gets up there and rescues the friend. Now, reporters from a news network arrive at the scene and acknowledges Madame Foster. Bloo whines that he does do good deeds all the time, so he waxes the floor (everyone who walks on it slides and injures themselves) to prove his point. Since he filmed himself, he sends the tape to a news channel. Instead of congratulating Bloo, he actually becomes embarrassed. Bloo tries another tactic to prove that he can do good deeds: building another home for imaginary friends called Bloo's Foster's Home for Imaginary Friends.

When a pen that looks like Abraham Lincoln is caught with a student cheating on a test by Mac's teacher, he is saved by Mac and Blooregard along with his au pair, a green ogre type. The Lincoln pen cons Madame Foster into a new plan to adopt an overcrowded home to unsuspecting adoptors for a fee, then take over the house and plan to turn the home into a casino. Mac finds this out the hard way as Wilt becomes a flagpole and Eduardo becomes a shell of his former self, as it were, and is put with Mr. Herriman and Frankie in a locked closet. What will Bloo do to save the house, and will Madame Foster get control of the house back?

In her sleep, Goo accidentally creates all the villain characters from a make believe game that she had helped out on while the power was out at the home during a thunderstorm, who then imprison Mac and Bloo at the home. Now, the gang must finish the game to save their friends.

It's time for the Five Year Creator Reunion Picnic, where imaginary friends' creators come to Foster's to see their imaginary friends. However, once again, Wilt's creator doesn't show up. So he sets off on a cross-country journey to find his creator. But soon Mac and the gang find out that Wilt had gone missing and set out on a road trip to find him. But Bloo's ridiculous theories of to Wilt's disappearance leads to many twists and turns in the journey to find Wilt. Will Wilt ever find out why his creator doesn't show up? Will Mac and the gang find Wilt? Will the lot make it out in one piece?