Wee Boo is a ghost who wants nothing more than to earn her haunting license like all the other accredited ghosts. The problem? She's far too cute to scare anyone! She's given one last chance, with extraordinarily low standards: Boo doesn't need to make anyone scream or gasp or shudder, she just needs one "whoa" to earn her place as a certified ghost. But she's running out of chances and her final haunting is not going well--that is until she meets a baby. When Boo makes the baby laugh, she realizes something: although she's terrible as a scary ghost, she might just make an outstanding imaginary friend. And a baby laughing in a crib at an invisible friend might just be enough to spook someone after all--the baby's parents.