"X" is the twenty-eighth episode of the Teen Titans series and the second 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 Zynothium, 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 Zynothium in the first place, and forces him to reveal the most likely location where more Zynothium 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 Zynothium 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 Zynothium 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 Zynothium, 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 Zynothium at their feet, using the detonation to cover his getaway. While Chang, his gang and the Zynothium 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.
- 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.
- 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.
- 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.
- This episode has the shortest title out of any other episode in the series, having only a single character.
- 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.
- 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.
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