Of course he opens it. The thought of losing Rose once had almost stopped his hearts. No way could he do it a second time and survive. That makes it easy to stare down van Statten while his mind cooks for another plan.

And then Adam points out that he's got weapons in his catalog room. Most of them are broken (or, in extreme cases, hair dryers), but there's one. And one's all he needs.

He bounds up the stairs to the top level. Rounding the corner, he sees Rose and the Dalek, and he shoulders the gun. As distasteful as it would have been to him to hold something like this before the war, that's how good it feels to hold it now, just a flick of the finger away from the destruction of the last Dalek in existence.

"Rose, get out of the way!"