When Henry gets a call from his friend, Patrick, inviting him to a sleepover party, Henry and Mudge know that fun galore is in store. From monster movies to flashlight surprises to tubs full of popcorn, this party is sure to be the best of the year! And when Patrick's dad leads all the boys (and all their dogs) up to the attic, Mudge turns out to be the biggest party animal of all. But the real question is, will this crew ever get to sleep?