‘That's right, isn't it?’ Harry urged him

‘That's right, isn't it?’ Harry urged him. ‘You died, but I'm talking to you ... you can walk around Hogwarts and everything, can't you?’

‘Yes,’ said Nearly Headless Nick quietly, ‘I walk and talk, yes.’

‘So, you came back, didn't you?’ said Harry urgently. ‘People can come back, right? As ghosts. They don't have to disappear completely. Well?’ he added impatiently, when Nick continued to say nothing.

Nearly Headless Nick hesitated, then said, ‘Not everyone can come back as a ghost.’

‘What d'you mean?’ said Harry quickly.

‘Only ... only wizards.’

‘Oh,’ said Harry, and he almost laughed with relief. ‘Well, that's OK then, the person I'm asking about is a wizard. So he can come back, right?’

Nick turned away from the window and looked mournfully at Harry.

‘He won't come back.’

‘Who?’

‘Sirius Black,’ said Nick.

‘But you did!’ said Harry angrily. ‘You came back—you're dead and you didn't disappear—’

‘Wizards can leave an imprint of themselves upon the earth, to walk palely where their living selves once trod,’ said Nick miserably. ‘But very few wizards choose that path.’

‘Why not?’ said Harry. ‘Anyway—it doesn't matter—Sirius won't care if it's unusual, he'll come back, I know he will!’

And so strong was his belief, Harry actually turned his head to check the door, sure, for a split second, that he was going to see Sirius, pearly-white and transparent but beaming, walking through it towards him.

‘He will not come back,’ repeated Nick. ‘He will have ... gone on.’

‘What d'you mean, “gone on"?’ said Harry quickly. ‘Gone on where? Listen—what happens when you die, anyway? Where do you go? Why doesn't everyone come back? Why isn't this place full of ghosts? Why—?’

‘I cannot answer,’ said Nick.

‘You're dead, aren't you?’ said Harry exasperatedly. ‘Who can answer better than you?’

‘I was afraid of death,’ said Nick softly. ‘I chose to remain behind. I sometimes wonder whether I oughtn't to have ... well, that is neither here nor there ... in fact, I am neither here nor there ...’ He gave a small sad chuckle. ‘I know nothing of the secrets of death, Harry, for I chose my feeble imitation of life instead. I believe learned wizards study the matter in the Department of Mysteries—’

‘Don't talk to me about that place!’ said Harry fiercely.