The Alden children are searching for a rare comic book of their favorite superhero, Captain Fantastic. They finally find the comic and something else, too—a strange note inside, "signed" by the comic's creator. The Aldens realize the note is a fake. But when they start to investigate, the mysterious note is stolen! It looks like someone wants to sabotage a superhero. The Aldens will need their super powers of investigation to catch this comic book culprit!