Harry could have sworn it started the day after Fred, Lupin and Tonks had died. He could have also sworn that he had nothing to do with it, although no one tried to incriminate him. But he felt sick when he heard that they had seen Snape at night in the Slytherin common room.

Any attempts to find out who exactly had seen him and what the Professor had been doing there ended in nightmare. All Slytherins, from a first-year to Goyle, readily confirmed that the former Head of the House spent his nights sitting on a sofa in the Slytherin common room, speaking to no one, and left silently with the first rays of dawn, disappearing into the wall. Until the next midnight.

'He could not have become a ghost,' Harry said despairingly to Ron and Hermione. 'I'm sure, he couldn't.'

'Nearly Headless Nick assures that no new ghost appeared in the castle,' Hermione replied. 'It's a fib.'

'A fib?' Ron laughed. 'Everyone tells the same. They saw him there.'

'They lie,' Harry replied quietly. 'Snape couldn't have stayed here. Besides, Nearly Headless Nick wouldn't have lied to Hermione. Ghosts haven't heard about him, which means Slytherins made it up.'

But rumours about Snape's ghost were so fascinating that the news had spread around the school in a flash, and even the teaching staff was infected. When the Ravenclaw fifth-years asked Slughorn about it in Potions, the Professor hesitated, but finally admitted to seeing Snape; and Trelawney related what Snape supposedly told her, in a tragic whisper, to anyone willing to listen.

In several hours the tales about the former Head of Slytherin House reached utter absurdity. Harry, Ron and Hermione learned about it from Luna Lovegood on their way to dinner.

'No one knows when he died,' Luna's face was shining with absolute happiness. 'Yesterday Draco Malfoy told that all the previous year Hogwarts had a ghost Headmaster.'

'What the hell!' Harry exploded. 'Are you guys mad or what? I saw him the day before yesterday! He was killed by Voldemort!'

It was not wise of him. Hannah Abbot was passing by and decided to contribute to the conversation.

'How can you be so sure who has killed him and when?' she asked. 'No one knows.'

Harry recognized the argument to be pointless and regretted his rash words, but Ron didn't want to give up.

'Snape was killed by Voldemort yesterday,' he stated flatly. 'His ghost couldn't have been the Headmaster.'

'Well, Pansy Parkinson said she smelt rat since September,' Hannah shrugged and left for her table.

'It's another Slytherin plot,' Harry spoke through clenched teeth. 'Malfoy is behind it.'

'What for?' Hermione inquired reasonably.

'Because he's a jerk,' snapped Ron. 'There's no ghost.'

'Everyone knows that Professor Snape has become a ghost and haunts the dungeons,' Luna stated calmly. 'They saw him there. They even say that it was Harry who ordered him to stay in the dungeons, to keep him from scaring first-years. But I don't believe this.'

And she proceeded to the Great Hall, paying no heed to Ron's flabbergasted expression.

'And yet she believes we had a ghost Headmaster!' Ron exclaimed. 'Hell, we cannot even prove anything now.'

'Three days are not enough to create a legend,' Hermione said thoughtfully, looking after Luna.

'As you can see, it is enough for us,' Harry snapped, angry at Slytherins in general and at Malfoy in particular. 'Ron is right. There's nothing we can do about it now.'