Who betrayed us?

MUTOID: Stay where you are. [Travis moves forwards]

TRAVIS: Which of you is Avalon? [He holds a nearby man and places his gun to the man's head.] I want Avalon -- now. [A figure moves forward. Another puts out a hand to stop her, but she continues forwards. Travis hits the man he was threatening, knocking him over.]

AVALON: Who betrayed us?

TRAVIS: [To mutoids] Take her.

MUTOID: [Indicating homing beacon] Shall I smash it?

TRAVIS: No. Give Blake his homing beacon -- make it easier for him. Finish it.

TERLOC: No, no, please wait. It's me, Terloc, I helped you. I gave you Avalon. I gave you Avalon. [The mutoid pushes him over with her foot] Ughh. Uh, ah. They're going to kill us. [Mutoids systematically shoot everyone amid lots of screams and shouts, then leave.]

Original via Lisa ...

Avalon is played by Julia Vidler.
Blake's 7, Season 1, Project Avalon.