Shocked, a tad pleasantly, he was scared to admit, that the man had let him off, as it were, he ran off quickly so that the professor did not have chance to change his mind.

However, as he rapped on the door behind which he knew his sister was, he could instinctively tell that something was not right. As she answered the door and her face dropped, obviously showing that she'd expected it to be someone other than him, he felt her crash into his arms, in tears, clutching at photos of what looked like Kristi, her mother and....Snape.

It clicked as she looked up at him, eyes sparkling and whispered, "She's dead and now I've wrecked everything. I've barged in on them like some common scarlet woman. Everything that's tearing them apart is all my fault."

She then told him everything, to do with Darrin, to do with Snape and to do with Kristi.

It was only after she had done all this did he have the strength to leave her side and dash back to the potions classroom.

I'm having a blonde moment, Snape did discover all of Darrin's dirty dealings didn't he?