Louis wasn't going to hang back this whole time, and anyway, he suspected that Remus was well aware that Bellatrix wasn't alone. He scrambled to his feet and came out just as the black dog appeared and turned back into Sirius Black.
"It's my fault," he said quickly, still mostly focusing on the fact that a very large wolf seemed to be facing off with Bellatrix. He glanced nervously to Sirius before trying to explain. "I brought her here. I didn't mean...We weren't going to do anything, really." This was definitely not the way he'd hoped to meet Sirius Black.