It wasn't that he had forgotten that Rodolphus was here. It was just that he was caught up in everything that was happening, and it wasn't as if Rodolphus had done anything recently anyway. He didn't think they were safe, but their lives were returning to something normal. And Sirius could deal with that.
And so in a way, he was entirely unprepared for the sight of James and Rodolphus talking. Something inside him went hard and a cold, and he could feel fear rising up in the back of his throat. But it was like when he had fount that Remus was in the bottom of the lake. Instead of giving into the onslaught of emotion, he just had to act.
Before he began walking forward though, something inside of him simply shifted. He'd been trying to capture the sensation for weeks, trying to sort out what it was that had made him Padfoot. And it was -- something inexplicably, but utterly him. Without warning, he was rushing forward on four legs, a blur of black fur. He barked sharply at Lestrange just once before sinking his teeth into the back of the man's leg, intent on getting him away from James and damn the costs.