The Doctor strides confidently into the middle of the studio, his hands in his pockets, whistling loudly. "Come on, Ponds, we're going to..." He spins around as the door slams behind him. A lock slides into place.
And then he realises.
His hearts sinking, he turns to the right, and sees a mirror covering the entire wall. In the reflection, the room is darkly lit by a single, flickering bulb. He isn't there.
But the angel is.
He wants to scream in frustration, to cry until he has no tears left. How could he have fallen into such an obvious trap? He can't believe it. He can't believe how stupid he's been. The angel's head is slightly tilted, as if mocking him. A hint of a smile is visible through its hands, cupped over its face. He stares, even though he knows there's no way out this time.
The mirror is a reflection of the real room. The one he walked into was an illusion, just to hide the truth from him. The angel is really there, and although he is too, he's been edited out of the picture. They can get to him faster that way, if he's got no sense of placement. That way, he won't be able to gauge how close he is to the angel. It could be right behind him right now, just inches away, and he wouldn't know – because he doesn't know where he is.
He can't move in case he touches it. It could be in front of him, behind him, to his left, to his right. Every way he turns, death is smirking right in his face. And yet he has no way of telling it's there until it happens. He just stares straight at the mirror. There's nothing else to do – it's the only way to see the angel. If he looks away, it will move, and then he has no chance.
His eyes are beginning to water. He closes one and then the other, giving himself little relief. Just moments later they're burning, and he opens and closes in a cycle, desperate to keep his eyes open but desperate to close them, too. The angel just stands there in his direct, fluttering vision, making a fool of him. He stops, swallowing hard. He can't do this for the rest of his life – which he's sure is how long he'll be here.
The angel's going to get him at some point or another, whether now or in hundreds of years. It's just his decision when.