X is the 28th episode of the Teen Titans series and the 2nd episode of Season 3.
Robin's past comes back to haunt him when the Titans are shocked to see the return of a villain they never thought they see again... Red X. It turns out that someone has stolen the suit and has now donned himself Robin's old villain identity and is out to gain himself a rare but dangerous chemical that powers the suit. Now Robin must face his past mistake if he and the team stand any chance to stop Red X, but Red X isn't the only thing they need to worry about as soon something much worse will threaten the city.
The Titans attempt to stop a break-in of a warehouse - only to find the burglar to be none other than Red X. Despite the Titans' best efforts, Red X manages to steal a device and get away, even though his power belt briefly malfunctions.
As it turns out, the Red X suit has been stolen from the vault in which Robin had locked it because he was unable to destroy it. To top off the good news, Robin reveals that the suit is powered by a dangerous substance called Xenothium, and that Red X is likely trying to use the stolen scanner to locate more of it. In order to rectify his biggest mistake, Robin seeks out the criminal scientist Professor Chang, who had helped him in procuring the Xenothium in the first place, and forces him to reveal the most likely location where more Xenothium is stored: a tech company on the city's south end. Robin informs the other Titans, but before Cyborg can get there, he is ambushed and incapacitated by an unknown assailant. Arriving at the place, the Titans encounter Red X but are again unable to stop him, and Red X penetrates the facility. Robin tells the Titans to split up, but one by one Beast Boy, Raven and Starfire are taken down - and not by Red X.
In the meantime, Robin finds and chases Red X, finally cornering him in the Xenothium storage vault. Their fight is interrupted by a group of men in HazMat suits, who turn out to be Professor Chang's henchmen. By breaking into the facility and disabling the most crucial security systems, Red X and Robin had enabled Chang to get the Xenothium he needed to power his super disintegrator cannon, which he intends to use to take revenge on the city. In order to ensure no interference from Robin, he had his men capture the other Titans, who are standing, flash-frozen, in his headquarters as hostages.
Despite Red X's taunts, Robin imprisons him and sets out to rescue his friends. Just as Chang prepares to fire the cannon, Robin interferes, with only the top portion of Titans Tower getting hit, but ends up helpless before the gun's muzzle. Suddenly, Red X appears, disabling the cannon's controls, saving Robin and helping him in bringing down Chang and his henchmen. Red X takes a vial of Xenothium, planning to use it to power the suit, but much to his surprise finds that Robin had taken his power belt from him. As the Titans try to take Red X to jail, he throws the vial of Xenothium at their feet, using the detonation to cover his getaway. While Chang, his gang and the Xenothium are returned to their rightful places, Robin muses darkly about the clarity of the lines between good and evil.
- After their first fight with Red X, the Titans gather on top of the warehouse. Behind them, in bright lights, is the term "SOTO", presumably the company that uses the warehouse. It is also the name of Alex Soto who directed several episodes.
- When Beast Boy presents his theory about the new Red X's identity
- One of the choices he presents is Jason Todd, one of the past Robins in the DC comics, one was Nightwing (future Robin) and one was Larry. Due to many similarities hinted at in the series, Todd is believed to be the most likely choice for the new Red X. See Red X - Identity for details.
- One of Beast Boy's possible choices for Red X's alter ego is "part of a clone army". If you stop at the right time, you can indeed see Robin wearing a Star Wars clone trooper armor suit (sans helmet).
- Another possible choice is a "long lost brother". In Batman Forever, Dick has an older brother named Mitch who was killed by Two-Face along with their parents.
- Silkie makes the first of his plot-hole-inducing cameos by being launched into the air after Beast Boy and his board of theories are tossed by Raven. He is shown slinking away off-screen on the counter top and possibly very much in view of Starfire, who appears to look on in shock as Raven gives her own theory for who Red X is.
- The episode Masks is referenced, with the Titans believing Red X to still be Robin and that he's a hologram or robot.
- The dove flying by during Robin and Red X's moment of teamwork refers to the likes of directors John Woo and Ridley Scott, who have used the dove imagery in their films.
- Red X pulls on Robin's mask, which pulls the flesh and skin around his eyes along with it as if it was glued on, and lets it snap back into place. In the DC comics, Dick Grayson (at least as Nightwing) indeed uses spirit gum to keep the mask on his face.
- Towards the end of the episode, a significant amount of Starfire's hair is burned off from a blast from Chang's disintegrator cannon.
- This episode is seen as having a major point, in Robin realizing it is sometimes hard to determine if a person is good or evil.
- Robin: It's simple: There is good and there is evil. There are those who commit crimes and those who stop them. The two sides are opposite, as different as day and night. And the line between them is clear... Or at least, it's supposed to be.
- Red X: Come on, kids. X marks the spot.
- Robin: [Starfire pokes him] Ow! Hey! Star! Ow! That hurts.
Starfire: Then you are not a hologram?
Starfire: [continues poking him] The last time we faced the Red X, he was you in disguise and you were not really there.
Robin: STARFIRE, CUT IT OUT!!!
Starfire: He is not a hologram.
Beast Boy: He could still be a robot. [to Cyborg] Check him for batteries!
[Cyborg snaps on a surgeon's rubber glove to perform a rectal exam]
Robin: Wait! Please! [everyone stares suspiciously at Robin] It wasn't me! I promise! It wasn't me! [silence] Red X was a mistake. A mistake I won't ever make again.
- Red X: What's the matter kid? Don't you wanna play? After all... they're your toys.
- Robin: I thought you didn't like playing the hero.
Red X: Doesn't mean I don't know how.
- Robin: There is good and there is evil, but the line between them can be almost impossible to find. Does one good deed make him a hero? Am I to blame for all of it because of a single mistake? All I know is that the answers don't come easy. It's supposed to be simple, but its not.
- Robin: Who are you..
Red X: If I wanted you to know that would I be wearing a mask?
- Red X: You know cutie the only crime here is that we haven't gone on a date.
- Robin: I'm supposed to be one of the good guys. To always do the right thing. The line was supposed to be clear. But for me, back then, it wasn't. A mad-man was threatening the city and I had to stop him. So, I became Red X. A ruthless thief who could get closer to the mad-man than Robin ever could. But I didn't tell my teammates and my plan didn't work. I almost lost my life and my friends. It was the closest I've ever come to crossing the line. And I thought it was in the past. But now, someone else has crossed that line and it's my job to stop him.