Love how when they're all locked in the cellar in Malfoy Manor, Harry doesn't even think of attacking Draco when he comes down into the cellar. Even though he and the others are loose by then and they could probably have easily overpowered Draco and taken his wand - as they do immediately when Pettigrew comes in.
They could've overpowered Draco, Imperiused him with his own wand, and sent him back up to give some excuse while Dobby evacuated the others. But that would've put Draco in terrible danger. It would've meant attacking and potentially injuring him. It also would have meant that he would be blamed for the resultant escape, vastly increasing the likelihood that Voldemort would kill him. And Harry simply cannot bring himself to hurt Draco or put him in danger.
So when Draco comes down Harry does nothing. He doesn't even speak to him to try to shame or manipulate him as he does when he tells Pettigrew that he owes Harry his life. Even though Harry witnessed the scene on the Astronomy Tower and he knows that Draco isn't happy with his lot and is experiencing a lot more doubt and conflict than Pettigrew is, he says nothing to Draco and just complies with him. Thus keeping him out of a situation that could put him in danger.
And Draco, for his part, sees that Harry and Ron have already managed to escape from their bonds but doesn't report it when he goes upstairs. He takes Griphook, who confirms Hermione's story, thus saving her from being murdered on the spot or tortured more. And he says nothing about the fact that Harry is free, possibly planning an escape.
He didn't identify Harry. He turned his back on Ron and Hermione and refused to confirm their identities either, even though this behavior was very notable and suspicious given that they are not disguised and other recognize them. And when he sees that Ron and Harry are already loose in the cell, not still bound as they are meant to be, he says nothing.
He's probably sick with fear and horror, certain that there's no possibility of escape, and probably cursing himself for taking these risks and not simply doing everything he can to get his family back in Voldemort's good graces. But somehow he still hopes.
