Mustard shouldn't still be here, but he is. Imaginary friends don't normally stay with their person until that person is a teenager. Imaginary friends don't suddenly become visible to their person's mom and then go on a date with them, either. But when those people—such as the troubled Thai and her dangerously upset mother, Sadie—need help, they’re lucky that Mustard's there with a goofy smile on his face. But Mustard has his own peculiar problems. Since he's still around, he has to abide by some rules enforced by unsavoury characters. And, oh yeah, he's falling in love with Sadie, who doesn’t believe he's real. For someone whose purpose was once so simple, Mustard sure has a lot to deal with.