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!