The Doctor is just about to leave when she calls out.

"Being outside the vault-" The Mistress cuts off abruptly. The Time Lord turns but she is facing away, seemingly staring at an unremarkable patch of flooring.

"What is it?" He asks, cautiously taking one step towards her. She does not reply.

"Missy?" The Time Lord murmurs. She stands frozen, breaths coming out slightly faster than normal.

He walks until he is just behind her and takes her arm in his hand, gently turning her towards him. She does not resist but her head tilts away from his gaze. He runs a thumb over her arm as her jaw clenches.

"Missy?" He asks again. The Time Lady still doesn't react and he carefully places his hand not wrapped around her arm against her cheek, tilting her face up towards him.

"It was terrifying." She says in a small voice, opening her eyes to blink away tears. The Doctor pulls her in closer, letting his hand slide to her back and mimic the movement of his thumb with his whole hand.

"I could barely see the console in front of me. I don't know why. It just- being outside-" The Mistress shivers, face crumpling against her oldest friend's shoulder, "It was overwhelming." She cries quietly and the Doctor sighs.

"I know." He says solemnly.

"You only peered around the central column when you were certain I was there- you were waiting for me as an anchor- something that links you to in here. You were nervous. I gave Nardole what I was holding because I wasn't sure whether you were going to collapse or try and somehow convert the Ice Warriors into an army while you were there. You asked if I was alright because you started to panic. You were trying to turn your own focus on to the fact that I was there- distract your brain from the stress of the situation. You forgot you were at the Tardis console until I reminded you that you weren't supposed to be there. You accepted going back in here so easily because you were afraid. You asked again if I was okay because your own hearts were beating so fast that they sounded like the drums for a few seconds. You were so scared you let your shields slip. You almost passed out. Why do you think I let you drive?" He asks softly. She tries to bury herself deeper in his chest, arms still clutched tight around herself.

"You've been in here a long time." He says quietly.

"Please don't." The Time Lady says quietly, "Please don't say it. I don't think I could take it if you said it. The confirmation would be too much. Please stop." The Doctor sighs again, wrapping both arms around her now and letting his head rest against hers.

"I won't then." He says, breathing in the smell of her hair. He waits for a while.

"I swore to protect you. That means when this is over I'll help you overcome this." His voice is low as he presses a kiss to her head, "And then we'll see the stars, Mistress." He says gently, closing his eyes. The Time Lady manages to pry her arms from around her chest, gingerly wrapping them around him.

"Just you and me?" She asks, voice still fragile.

"Yes." He says resolutely, voice rumbling through the both of them, "Just us."