"I know what you're thinking, Mary Ann," Nyssa said, once the four of them had returned to their TARDIS.
"Do you now," Mary Ann said.
"Yes, you're thinking of trying to save your parents. Am I right?"
"Well, yes I am," Mary Ann said. "What of it?"
"You can't do it, Mary Ann. You can't change history, not one iota."
"Oh come on, Nyssa, this is not like strangling Hitler in his crib or stopping the Kennedy assassination," Mary Ann said defensively. "This is just about saving a simple Kansas farmer and his wife."
"None the less, the one lesson we learned from travelling with the Doctor is that you cannot change the past," Nyssa said. "Mary Ann, believe me, I know how you feel. I've told you how my home world was destroyed. Don't you think that, if I could, I would go and prevent it, but I can't. The damage to time could be catastrophic."
"Could be. You hear that, Nyssa, you're guessing," Mary Ann said. "You don't know for sure, do you."
"Well, no I don't. I just know what the Doctor has said, and he's a Time Lord. He knows what he's talking about."
"Yeah, well he's not here, is he," Mary Ann said as she stormed out of the console room. Soon the door to her bedroom could be heard slamming shut.
"Well, that could have gone better," Tegan said.
"I'll go talk to her," Gilligan said as he headed out of the console room and for Mary Ann's room.