This is season 4, episode 4 of Disney Channel's Wizards of Waverly Place.
In this Wizards of Waverly Place episode, Journey to the Center of Mason, Mason's jealousy erupts when Alex's ex-boyfriend, Dean returns. Alex, Justin, and Max have to rescue Dean when Mason eats him.
This Wizards of Waverly Place episode begins with Alex (Selena Gomez), Mason (Gregg Sulkin), and Harper (Jennifer Stone) walking into the sub station. Jerry (David Deluise) quips that instead of breaking up, Alex and Mason became "just friends." Alex talks about the perks of being just friends. She doesn't have to worry about her breath. Theresa (Maria Canals Barrera) laments on how werewolves can't date mortals, and she feels like she's in a horror movie.
Alex says that nothing can get in the way of her friendship with Mason. Dean (Daniel Samonas) walks in and announces that he's back. He asks Alex if she wants to smooch.
Alex is surprised that Dean is because she thought he had moved to Ohio. Alex explains to Dean that Mason is a friend, and a boy, but not her boyfriend. Dean wants to get back together.
Max observes that Deam is all over her. Mason tries to brush it off, but is starting to feel jealous.
At the lair, Justin (David Henrie) introduces a new delinquent student, a girl named Tyler. Felix is late because he was called to WizTech to give Justin a note. Felix takes his seat next to Tyler while Justin reads the note.
Because of Felix's progress, Justin has raised his standing in the wizard competition, but he still needs to raise the standings of the rest of the class.
Alex explains to Mason that she had dated Dean over a year ago. They find a trail of petals leading to a ski ball machine. Dean remembers to their second date. Alex and Dean are having a good time playing ski ball, and Mason feels left out.
Justin is inside a microscope because he had taught Felix the up and atom spell. Justin asks Max to get him out of there. Justin asks the class to concentrate. The sooner they can get back into WizTech, and the sooner he can raise his standings in the wizard competition, the sooner they'll never have to see each other again.
At the sub station, Mason tells Max that Alex still has feelings for Dean. Max thoughtlessly remarks that Dean still has feelings for her too. Outside at the ski ball machine, Dean offers to pick up some snacks before their rematch.
Harper, Jerry, and Theresa walk by and happily see the ski ball machine and want to play. Harper asks Alex how Mason feels about Alex playing ski ball with Dean. Alex says that she and Mason are friends and that he wouldn't have a problem with friends playing ski ball with other friends.
At the sub station, there is a growling noise. Mason has turned into a werewolf. Max tells Alex that Mason has eaten Dean. Max thinks it's the coolest thing ever.
Mason apologizes and explains that he just got a little jealous. Alex yells at him. "That doesn't mean you can eat him!" Alex asks Justin to help because Mason ate Dean. The class think it's funny. Tyler suggests that everybody shrink themselves down, go inside Mason, and play around his stomach until he belches up Dean.
Justin actually likes Tyler's idea. Justin, Alex, and Max use Captain Jim Bob's submarine and cow costumes. Justin turns the abracadoodler int oa submarine tracking system so they can figure out where they are in Mason's body. The class will shrink them, and Mason will swallow them.
Suddenly there's a beeping noise. They're going the wrong way towards his head. They are now in Mason's brain. They get to see the images of Mason's thoughts--they're all of Alex. She thinks it's sweet that he's always thinking of her.
They are finally going the right way, but Max keeps turning on the windshild wiper. They finally made it to his stomach. They find Dean and pull him into the submarine. He's out cold but still breathing. He's covered in oatmeal. Alex and Mason had had that for breakfast.
Alex asks Harper to get them out of here. Justinb tells Harper to make Mason burp and for Felxi to catch whatever came out. The class successfuly uses the spell to bring them back.
Justin carries Dean out of the lair and back into the sub station. Dean wakes up and asks what happened. Alex tells Dean that he was knocked out by a bowl of flying oatmeal. Dean still wants to get back together, but Alex wants to be with Mason. Dean leaves graciously.
Mason reminds her that if she's going to be mortal, then they can't be together. Alex decides to reenter the wizard competition. She wants to win for her and Mason.
Jerry and Theresa are enjoying a game of ski ball. Alex informs them that she has decided to get back in the wizard competition and to win. They are too wrapped up in ski ball to listen. Jerry gives her $20 for candy. Mason tells them that he ate Dean, and they stop in shock. Alex tells Jerry and Theresa that Mason had said they were going to the movies. Alex and Mason run.