Betrayal is the 23rd episode of Teen Titans series and the tenth episode of the second season.
The episode opens on a power plant being robbed by Slade's robots. They are about to make their escape when they are stopped by the Titans, including Terra. The Titans swiftly defeat the thieves, with Beast Boy coming to Terra's aid in the midst of the battle. Later, Slade is in his lair observing images and videos from the battle, as well as weapons and paraphernalia belonging to the Titans, supplied to him by an unknown character. Slade congratulates his accomplice and says to stick to the plan and by tomorrow the Teen Titans will be destroyed. The only clue to the identity of the mysterious figure is a bright blue eye staring out from the darkness.
Back at Titans Tower, the Titans award the last slice of pizza to Terra for her superb efforts and mastery of her powers and throw a small party for her. She tries to shrug it off, saying it's no big deal. Beast Boy says that good friends like her don't come along every day. Cyborg locks down the Tower and the Titans retire for the night. Terra goes to her room and sends off an e-mail to an unknown character before Beast Boy knocks on her door. Although nervous, he presents her with a small package, declaring that he made something for her. Terra opens the package and finds a heart-shaped box with a mirror on the inside of the lid. Terra is moved and doesn't know what to say. Beast Boy replies, "You can say 'yes' because I'm about to ask you on a date." He asks her if tomorrow is okay, but Terra suddenly becomes mortified and abruptly retreats to her room saying, "I just can't". Back in his room, Beast Boy is busy reprimanding himself for not being more calm when asking her out, and thinking of different ways to change her mind; just when she appears outside his window, saying she wants to go out with him tonight. Just as they leave the Tower, Cyborg wakes up and goes to the kitchen for a snack, but finds an enormous army of Slade's robots waiting in ambush.
Terra takes Beast Boy out of Jump City to a small restaurant where she frequently visited before she became a Titan. They order food, but Terra quickly whisks Beast Boy off when she sees an image of Slade in the restaurant, unbeknownst to him. She pulls him away so suddenly that Beast Boy drops his communicator just as Robin begins calling him for help. The other Titans are fighting for their lives back at the Tower against an army of Slade's robots, realizing that Terra is gone as well. Cyborg cannot figure out how they bypassed his security and got into the Tower so easily. Meanwhile, Beast Boy and Terra are visiting an abandoned theme park. Terra seems rather distant and distracted. Beast Boy tells her that it's okay if she's not having fun with him, but Terra smiles and says that he is "her definition of fun". They both have a wonderful time riding bumper cars, playing games, and taking pictures together and form a close romantic connection. Later that night they are alone on the ferris wheel and Terra asks if Beast Boy would still be her friend even if he knew something bad about her, feeling that she can trust him to be a real friend. Beast Boy promises her unhesitantly and is about to kiss her when Slade appears and attacks.
Beast Boy fends Slade off by himself as best he can and the fight ends with Terra bringing the Ferris wheel down on top of Slade as Beast Boy escapes the wreckage. They then take refuge in the house of mirrors where Beast Boy realizes he has lost his communicator. He says that they have to get back to Titans Tower, but Terra says she is not going back. Slade reappears and states that Terra has become his apprentice. Beast Boy fiercely asserts that he is lying, but Terra confirms it to be true. Flying into a rage, Beast Boy attacks Slade with all his might while Terra retreats to another part of the house. She becomes distraught and regretful, apologizing to Beast Boy and saying that she didn't want any of this to happen. Beast Boy appears, angry at her betrayal and that she had been pretending the entire time. Terra reminds Beast Boy of his promise to always be her friend, but he turns his back on her and says that she has no friends. Stricken at this, Terra leaves with Slade.
The next morning, Titans Tower has been torn apart, but all of Slade's robots and machines have been destroyed. The Titans are dejected over Terra's betrayal and Starfire says that the outcome does not feel like a victory. The final shot shows Beast Boy in Terra's room, curled up on the bed as a dog with the heart-shaped box he made for her, heartbroken over losing Terra.
- The title refers to Terra betraying the team's trust for Slade.
- The scene when Terra destroys the Ferris Wheel & tells Beast Boy to fly is probably a call back to Beast Boy's past. In the comics when Beast Boy & his parents where caught in a flood & Beast Boy's Mother told her son to fly to save his life. The bird that Beast Boy changed into was a small Bird, the same kind that he changed into in this episode.
- Robin: Tell Slade the Titans have a message for him.
Terra: Eat dirt!
- Terra: Beast Boy, if you knew something bad about me, would you still be my friend?
Beast Boy: Of course.
Terra: I mean, if you were really my friend, I could tell you anything. And no matter how horrible it was, you'd still like me, right?
Beast Boy: Yes. I promise, Terra. No matter what.
(He leans in, about to kiss her)
Slade: Hello, Terra. Remember me?
- Terra: No! I won't let you hurt my friend!
Slade: Dear child, you don't have any friends.
- Terra: Beast Boy, I'm sorry. I'm so sorry. I never meant for any of this to happen (while cluctching head and kneeling on the floor).
Beast Boy: Then why did you let it?
Terra: I don't know, okay? I don't know. Slade, he helped me. Saved me from myself. He said I owed him...
Beast Boy: So, it was all a game? You were just pretending?
Terra: No. You said you'd be my friend no matter what, remember?
Beast Boy: (Turns away from her) Slade was right. You don't have any friends.
- Beast Boy: (talking to himself) AAAHHH! You idiot! How could you mess that up?! All you had to do was knock on the door and say: (Muscular Beast Boy) "Hey Terra...You? Me? Movies? Friday?" (French Beast Boy) "You are the most beautiful woman I have ever seen..." (Greaser Beast Boy) "You wanna go for a ride on my moped?" (Puppy Beast Boy) "Woof! Woof!" (Dramatic Beast Boy in the rain) "PPPPLLLLLEEEEAAAASSSSEE???" Anything would've been better than giving her a stupid glue-covered box and acting like a total goober! Now she'll never go out with me!
- Starfire: They are too numerous to fight! What shall we do?
Robin: Fight anyway.
- Beast Boy: This is the greatest pie in the History of Pie.
- Raven: That's my room. (smashes Slade commandoes with pieces of wall) Nobody goes in my room.