TEGAN: Oh, great. You make it sound like a shopping list, ticking off things as you go. Aren't you forgetting something rather important? Adric is dead.

NYSSA: Tegan, please.

DOCTOR: We feel his loss as well.

TEGAN: Well, you could do more than grieve. You could go back.

NYSSA: Could you?

DOCTOR: No.

NYSSA: But surely the TARDIS is quite capable of-

TEGAN: We can change what happened if we materialise before Adric was killed.

DOCTOR: And change your own history?

TEGAN: Look, the freighter could still crash into Earth. That doesn't have to be changed. Only Adric doesn't have to be on board.

DOCTOR: Now listen to me, both of you. There are some rules that cannot be broken even with the TARDIS. Don't ever ask me to do anything like that again. You must accept that Adric is dead. His life wasn't wasted. He died trying to save others, just like his brother, Varsh. You know, Adric had a choice. This is the way he wanted it.

TEGAN: We used to fight a lot. I'll miss him.

NYSSA: So will I.

DOCTOR: And me. But he wouldn't want us to mourn unnecessarily.