"Sanctuary" is episode 19 of season 1 in the television show Angel. Co-written by Tim Minear and series creator Joss Whedon and directed by Michael Lange, it was originally broadcast on May 2, 2000 on the WB network.
In "Sanctuary", guest star Sarah Michelle Gellar returns as Buffy, who has come to Los Angeles seeking vengeance against Slayer Faith. Buffy is is shocked to discover Angel is attempting to redeem Faith's violent nature, and Wesley is faced with a crisis of loyalties when the Watcher's Council assassins offer him reinstatement if he gives Faith over to them. Also, evil Wolfram & Hart lawyer Lindsey approaches Kate to help them take revenge on Faith and Angel.
Downstairs, Faith confesses to Angel that she is haunted by visions of her violent past in Sunnydale. Angel talks to Faith about redemption, saying she has to make amends for her crimes, no matter how hard it is. Meanwhile, Wesley plays darts at a bar, and encounters Weatherby, a member of the Watchers' Council's Special Operations team on the hunt for Faith. The council members give Wesley an opportunity to come back to the Council if he's willing to turn in Faith. They give him a syringe that, if injected, will sedate Faith and let them take her back to England. Wesley agrees on the condition that Angel is left unharmed, to which the team reluctantly agrees.
The lawyers at Wolfram & Hart, upset that Faith has teamed up with Angel, hire a demon to have her killed. The demon sneaks into Angel's apartment and attacks. Faith kills it with a knife, and then is frightened by the sight of the demon's blood on her hands. Without warning, Buffy arrives at Angel's place and is shocked to find Angel hugging Faith.
Buffy is determined to turn Faith in to the police, but Angel objects and the two come to blows. Wesley arrives with the news that the Council is looking for Faith. The two Slayers escape to the roof, where they argue about everything that has happened. Buffy is unwilling to forgive Faith, even though Faith is genuinely sorry. One of the Council members attacks Buffy and Faith as another hovers above the roof in a helicopter. Inside the apartment, Wesley stabs Weatherby with the syringe while Angel runs upstairs and as the two Slayers seek cover against their attackers, Angel bursts through the roof skylight and gets inside the helicopter.
Detective Kate Lockley - guided by Lindsey MacDonald's information - arrests Angel for harboring the fugitive Faith. When Angel and Kate, with Wesley and Buffy in tow, arrive at the police station, they are surprised to see Faith is voluntarily confessing to her crimes. Later, Buffy admits to Angel how hard it was for her to see Faith with him. Angel counters by saying it was not about Buffy, it was about saving Faith's soul. Buffy lashes out by telling Angel she has someone else in her life, and unlike her relationship with Angel, she can trust her new boyfriend. Angel tells her it's good she can move on because he can't; he has no one to share his pain. Angel then tells her that she doesn't know him anymore and to leave L.A. Meanwhile, Faith manages to find peace in her jail cell.
Usually, Joss Whedon's name is listed first in episodes he has co-written and is credited for. In this episode, Tim Minear's name is listed first because he approached the editor and (jokingly) told him that his name comes first.
Joss Whedon has said that he explained the process of writing one of his scenes:
The last scene between Buffy and Angel in the crossover where she comes to Angel, that stumped us for a long time. And I finally realised when I was working on it that it's because they need to fight now. They can't be just like, 'Oh, we're swell pals and we get along.' They really are at very different places in their lives and it's very difficult for them to see each other. So it really helped define how the shows are different and it ends up with Angel laying into Buffy a little bit and saying, 'I've got my own show now, and it's different from your show, so get off my show!' That's basically what he's saying. And the moment I wrote that scene, I got very excited and I said, 'I get it now. I understand what Angel is and it's not Buffy,' and I felt like the training wheels came off.