"Sisters" is the second episode of the Teen Titans series.
Starfire's older sister Blackfire comes to Earth for a visit, while at the same time Starfire herself is getting attacked by an alien probes sent out to capture her. Starfire is happy to see Blackfire, but Blackfire being everything Starfire isn't, quickly starts to take her place on the team. Feeling they don't need her anymore, Starfire starts to think of leaving Earth for good. Will Starfire say goodbye to the Teen Titans, Will Robin be able to change her mind or Is there more to Blackfire then meets the eye?.
The Teen Titans are enjoying a fair when Starfire is suddenly abducted by an alien probe. The team succeed in fighting it off, but are left wondering where it came from. They return to Titans Tower, to discover Starfire's older sister, Blackfire, has stopped by Earth for a visit.
Starfire is initially overjoyed to see her elder sister, however her sisterly feelings change when Blackfire is well-received by the other Titans, and Starfire feels abandoned. Her attempts to restore her team's interest in her prove futile, and only sees the others getting further impressed by Blackfire. While attempting to spark the Titans' interest by having a movie night, Blackfire steals the attention by inviting them to a disco. Starfire is left alone when the other Titans manage to find partners for a dance. Robin tries to talk to her, but Blackfire drags him off. Starfire once again encounter the probes, which manage to overwhelm her. The Titans come to her rescue, where Blackfire destroys all the probes with light purple-colored blackbolts from her eyes. When Robin asks her how she did it, she replies with a hint of a smile that it was just a lucky guess. Cyborg remarks that they need that kind of luck and offers Blackfire a spot on the team. Starfire, who is still recovering from the attack, gasps in shock.
Starfire is sad about this at first, but then comes to the decision that the team will be better off without her, and decides to leave. Just when she is about to leave Robin appears and starts to talk to her but just then, the aliens who sent the probes show up and take Starfire captive. Robin attacks their ship and sets her free, but just as the other Titans show up and prepare to battle, the aliens announce that they are Centauri police, here to capture a Tamaranean thief, who they say is Starfire because she's a Tamaranean and because she was wearing the Centauri Moon diamond that Blackfire gave her, but she'd never even been to the Centauri Moons. But the Titans know who has been to Centauri and that there's another Tamaranean on Earth. Seeing the Centauri Moon diamond on Starfire, Robin realizes they must be talking about Blackfire because she's been to the Centauri Moons; that's where she'd gotten the diamond, and she told Starfire herself. It all turns out that Blackfire had stolen the diamond and gave it to Starfire and was only pretending to be the Titans' friend so she could get away with her robberies in Centauri and let her sister take her place in jail. The Titans find that Blackfire is trying to escape Earth to return to Tamaran. Starfire, enraged, flies after her sister, and engages her in combat long enough for the Centaurians to capture her. Blackfire is taken away by the Centauri Police, vowing revenge on her sister. The scene changes, and Starfire is shown sitting alone when Robin joins her. He encourages her by saying that no one will be able to replace her, which reveals a smile on her face.