Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and they're going to a comic book convention!   The Alden Children are searching for a rare comic book of their favorite superhero, Captain Fantastic. When they finally find the comic, they discover something else, too: a strange note inside, "signed" by the comic's creator. The Aldens soon realize the note is fake. But when they start