After seeing a scary movie, Huey, Webby, and Lena explore an abandoned subway line in search of a race of legendary creatures called the Terra-firmians, only to end up trapped underground with Mrs. Beakley, Louie, Dewey, and Launchpad. As they struggle to escape, Launchpad becomes more and more paranoid, leaving Dewey to help him come back to his senses. Meanwhile, Huey and Webby argue over the Terra-firmians’ existence, as Huey believes only in his Junior Woodchuck Guidebook and is afraid to do anything that does not follow its instructions. In the end however, the two reconcile and find out that the Terra-firmians are actually real. In the midst of their adventure, Lena struggles to gain Mrs. Beakley’s trust while secretly receiving instructions from Magica.