Peter Capaldi (Mr Frobisher) previously played Caecillius in the 2008 Doctor Who episode "The Fires of Pompeii".

Gwen: Who's back?
Jack: What's he doing?
Ianto: Waiting, just like you said. He's been there 20 minutes.
Jack: Persistent.
Ianto: Good sign.
Jack: Dogmatic.
Ianto: Always a plus.
Gwen: Oh, Christ, never work with a couple, you two talk like twins!

Dr. Rupesh Patanjali: My first case, my first death, was a suicide. Do you know why she did it? 'Cause she had written all these letters. She'd been a Christian all her life, and then alien life appears. She wrote this bit, she said, "It's like science has won."
Gwen: Lost her faith.
Dr. Rupesh Patanjali: More than that. She said she saw her place in the universe, and it was tiny. She died because she thought she was nothing.
Gwen: I went through that, even now I get terrified. But at the same time, it is brilliant. And beautiful. And completely bloody magic. It's bigger, you know. It's like... it's like the whole wide world is bigger. My life is bigger.

Dr. Rupesh Patanjali: What's in there?
Gwen: Big science-fiction superbase. Honestly! See you.

Gwen: Oh my God, Severn Bridge. I'm going in to England, farewell forever.
Rhys Williams: Good luck, have you got currency?
Gwen: Yes, and I've had my injections. See ya.

(to Jack)
Alice Carter: Yeah. I just can't stand it, Dad. I look older than you do and it's never going to stop. I get older and older and you stay the same. One day you're going to be standing at my funeral, looking just like you did when you were standing at Mum's. No wonder she was so furious. You make us feel old.

Timothy White: What's that thing?
Gwen: The technical name is a gizmo.

Dr. Rupesh Patanjali: He was dead.
Johnson: Now he's dead again. And we'll keep killing him till he's ready.