"I didn't say that I know what happened beyond what I've heard, just that I know how to fix it," Severus snapped, turning away from Lupin and looking down at the progress of their potion. He noticed that throughout the tense conversation, very little was getting done, so he went about drawing things over to his side and working on the steps as though he'd had the directions memorised; likely quite true.
He let Lupin's last question linger in the air, enjoying the crackle of tension that was building, some part of him hoping to see Lupin break under it. Unfortunately, he quickly looked over at his partner to see the strain on his face, and damn it all, he actually felt guilty again. With a long suffering sigh, he turned back to the potion and continued working to mask the deeper meaning of the words that he was about to speak.
"All I can tell you is that you need to bring Black to a secluded area, away from prying eyes, and let me do my work with him. I hate the idea of getting too close to that dunderhead, but if it means that I get to lord this over him, too, then I don't mind that too much."