I'm sorry, Clara is dead. Kate Stewart is dead. The UNIT troops are all dead. Truth or consequences.

Bonnie

Clara: Oh my God, that's me.
Jac: I think we should wait.
Clara: Look, they're here. They're growing duplicates of us. We have to destroy them. I've seen this happen before. It happened to that little boy. They took his parents and then they took him.
Jac: But I don't see how these are duplicates. That's not how Zygons work. They don't grow duplicates. They kidnap the originals so, these... These are the humans!

The Doctor: Which one are you? Human or Zygon?
Osgood: I don't answer that question.
The Doctor: Why not?
Osgood: Because there is no question to answer. I don't accept it.

Kate: You left us with an impossible situation, Doctor.
The Doctor: Yes I know, it’s called peace.

Any living thing in this world, including my family and friends could turn into a Zygon and kill me. Any second now. It's not paranoia when it's real.

Walsh

Clara: So Osgood's been kidnapped, right? I thought Osgood was dead.
Kate: There have always been two of her, ever since the cease fire. We never knew which one was real.
The Doctor: Both of them.
Kate: Okay, which one was Zygon.
The Doctor: Both of them. They would have maintained a live link. They were both Zygon and human at the same time.

Osgood 1: The Zygons are a peaceful race.
Osgood 2: Their shape changing abilities should not be considered a weapon.
Osgood 1: It's a survival mechanism.
Osgood 2: They embed themselves in other cultures and live out their lives in their new bodies, in peace and harmony. Mainly.

Enemies are never a problem. It’s your friends you have to watch out for.

Me/Ashildr

Me/Ashildr: You've had an impact on this world. You've made waves.
The Doctor: Sometimes tidal waves.
Me/Ashildr: I'm flattered.

You didn't save my life, Doctor. You trapped me inside it.

Me/Ashildr

Sam Swift: Who's this, your sidekick? You got your dad as your sidekick?
The Doctor: I'm not his dad, I'm the Doctor.
Sam Swift: Is that the best name you could come up with?
The Doctor: What, says Sam Swift the Quick? Trying a bit too hard, isn't it?

The Doctor: Why are you still alone? What happened to the second immortality charge I gave you?
Me/Ashildr: No one's good enough.

Doctor Who Season 9 Quotes

What have we got? What do we know? It's not an attack. It's not an invasion because, well that doesn't come with a fair warning. So, somebody needs our attention. Somebody who needs to put a gun to our heads to make us listen.

Clara

The Doctor: Tell me the name of the boy who isn't going to die today.
Boy: Davros. My name is Davros.