Does anyone else think Padma and Seamus seem unusually worried about him? They must have come up with one hell of a fake challenge, if his absence has got them this worried. And what does it have to do with Milland (Snape)?
Of course in a pinch, the real Milland could turn up dead. That would kill any suspicion and leave Snape free to move elsewhere. While most of the Order would draw the line at murder, I could see Snape doing so because he truly believes it the lesser of 2 evils, if he felt his continued freedom was essential to the fight against Voldie.
no subject