When a cavity forces Ben to the dentist, his day gets even worse when the malevolent magician Hex uses a nearby dream catcher to bring Ben's fears to life.
The episode begins with Hex somewhere seeking a magical artifact he's been searching for years. He finally finds it. Meanwhile, the Tennysons are driving looking for something to eat. Max passes a place that Ben wants to eat at. Ben questions what's so special about the place they're going, and they finally arrive. Gwen claims the place looks nice, however, Max states that's not where they're going. They walk down an ally. Max knocks on a door, and Melvin walks up asking for the password. Max says "avocado" and they're let in. Inside, Gwen compliments the smell of the place, and Max explains that the place is exclusive, and he had to make reservations 8 months ago. He then request three menus, but Melvin claims that they don't do menus. Ben and Gwen are annoyed at the presence of Melvin and Tevin. Melvin explains that the menus are etched into the counter top. Gwen points out they're hieroglyphs, and they can't read them. He then gives the three kid menus with pictures. Ben spots a deep-fried chocolate burger rolled in rock candy. Ben is given the utensils to eat it, but he throws them to the side and takes a bite out of it anyway. When he bites it, he screams as his tooth is now in pain. Gwen checks it out, and states that it's pretty bad. Melvin directs the three to the dentist next door.
The Tennysons walk to the dentist, and they meet Dr. Pang. Pang invites Ben into the dentist room. Max and Gwen observes the waiting room, and they find out that the dentist is an inventor. Dr. Pang tells Ben to look into a crystal as he works on his teeth. Meanwhile, Hex arrives in the room. Ben transforms into Diamondhead and fights Hex. Hex manages to take the crystal, and cast a spell that activates it. A portal to another dimension opens up, and sucks Diamondhead and Hex up. Diamondhead questions where they are, and Hex states that he brought them both into his Realm of Nightmares. There, he can make Ben's fears into reality. He claims that's only the beginning. He begins to make the portal even bigger, but Diamondhead interrupts. Hex drops him into a canyon. He then states that he will expand the portal until it engulfs the entire world. Ben times out as he falls into the canyon. His tooth still hurts, but he has to get to safety. Ben walks into a small cabin, and then he notices algebra on the board. He spots Mrs. Roland asking him to come to the board. Ben hits his watch constantly over and over again, and it breaks off. Roland then turns into Hex, and Ben runs away. He eventually runs into a maze, and there's tentacles around the place. Ben then walks through a door that leads to a abstract room of stairs. He is then hanging from the door nob. He states that he's useless without his powers, and he can't win. Suddenly, Cybearg shows up to help him. He explains Hex can only make bad stuff, but Ben can do the opposite.
While Hex is attempting to expand his portal, Ben and Cybearg attacks him. Hex, however, manages to beat them, and destroy Cybearg. Max and Gwen from the other side of the portal give Ben a quick pep talk, then Ben notices something. He finds out that Hex doesn't actually have control over the world, and Bens Omnitrix reappears and the portal changes color. ben transforms into Omni-Enhanced Cannonbolt and knocks Hex into one of his nightmares. Gwen tells Ben the portal is closing, so Ben summons Cybearg, and they both carry Hex out of the portal. Unfortunately, Hex doesn't want them to save him, so he escapes another way. Ben says his fianl goodbyes to Cybearg, and he lands back in his dimension. Later on, Bens tooth is finally fixed. Gwen is impressed that Ben conquered a lot of feats this day. However, Ben claims he still hasn't gotten over squids, and they're still the worst.