James was in glamours rather than Polyjuice; he wasn't going to risk either of his covers on a dangerous trip like this. And he was on guard, wishing for his Invisibility Cloak, but of course that had been lost with Remus. He hoped that they would be getting that back tonight.
The light of the spells aimed at them caught the corner of his eye, thankfully coming from far away enough that he had time to react. "Down!" he hissed to Sirius and Kingsley, dropping to the floor; one of the spells went over his head and hit the wall, leaving a burn mark. He was up on his feet again in a moment, heading for cover, not sure whether they had been caught or not. He was acting on the assumption that they had, however.