'He fears you,' said the demon at Sirius' back. 'He knows why you have come.'
'And how do you know?' snarled Sirius, not turning around.
'I see what you are holding in your right hand. Do you think you can slay a werewolf with such a blade? It is not silver.'
Sirius turned around slowly and looked at the demon with bleak black eyes. 'You'd be surprised how many things a knife to the heart will kill.'
'The Killing Curse is cleaner,' observed the demon.
'He deserves better than that,' said Sirius. He was still looking down at the knife, which he had taken from Lucius' armory because it was the finest weapon he could find, and because the opals in the hilt reminded him of moons, and it seemed fitting.
But in truth, it wouldn't matter what kind of weapon he killed his friend with. He would still be dead.
He'd do it for me, Sirius thought. But the thought lacked the resonance it had had before.
The demon chuckled. 'You cannot do it.'
Sirius ignored it.
'Perhaps,' said the demon, 'there might be another way?'
The demon shrugged. 'Very well. I did not come here to bargain.'
'What did you come here for?' snarled Sirius. 'You said you didn't come to kill Harry, but you tried to-'
'I was not trying to kill him! I was trying to warn him!'
'You attacked him!'
'I tried to make him listen. I tried to tell him that his life was in danger from the Snake Lord. But he and the other, the seventh son, they did not want to hear me.'
Sirius stood motionless, his heart beating hard. Surely the creature was lying — and yet- 'Why?' he demanded. 'What do you care what happens to Harry?'
The demon shrugged. 'We do not care. You are asking the wrong questions.'
Sirius took a step forward, his eyes fixed on the demon's red ones.
'Who are 'we'? What's your name, anyway? Do you even have one?'
The demon looked shifty. 'Very well. As a sign of good will I will tell you my name. It is Strygalldwir. Conjure with it and I will eat your heart and liver.'
Sirius doubted he'd be doing much conjuring with a name he couldn't even pronounce. 'So what does Slytherin want with Harry?'
demanded Sirius, and by reflex glanced down at the red jewel in his bracelet, which pulsed with a steady light. 'And what is the interest of Hell in these proceedings?'
'We are owed a life,' said the demon. 'The bargain made with the Snake Lord was that most binding of bargains: the gift of demonic power in exchange for-'
'His life,' said Sirius. 'After a set term of years. I get it.'
The demon giggled. 'Not his life,' it sneered. 'Who would make a bargain like that?'
'Then…?'
'The life of his heir. Specifically, a Magid descendant of his own blood. That was the bargain. That was why Slytherin, when alive, was desperate to produce an heir. Once he gives his own descendant's life freely to us, we have no choice but to consider the debt cancelled.'
'Draco,' whispered Sirius, and then, after a moment, realizing, raised his head and stared. 'Harry?'
'Why not?' Strygalldwir was grinning, showing more than one set of teeth. It was not a pleasant grin. 'Both boys are Magid descendants of Slytherin's blood. But the Potter boy also has Godric's blood in him. The Snake Lord needs to keep one boy alive and by his side, but the other will be a sacrifice. Slytherin's hatred of his cousin knew no bounds. He would consider it a nice irony to use Godric's heir for such a purpose. It will be as if Godric himself has set him free.'
'What do you care if he uses Harry to fill his bargain?' Sirius snarled. 'What difference does it make to you?'
'Because,' said the demon, red eyes whirling, 'this bargain was made a thousand years ago, when we were rich in items of True Magic and poor in Magids. The art of making Living Blades is long lost. That sword is one of two remaining in the world, and is far more valuable to us than the life of a Magid child. There are plenty,' added Strygalldwir, 'of Magids around these days. But we cannot take the sword back unless Slytherin forfeits his bargain. And he that will not happen until-
Sirius interrupted, shaking his head. 'In other words, you'd simply rather have the sword than Harry. Very nice.'
'I'm a demon. We're not interested in nice. Anyway, it's too late for Godric's heir. The Snake Lord has him now.'
Sirius' had was swimming. Why does Slytherin need one boy alive and by his side? he thought, and then he remembered Remus' voice, saying the words of the prophecy, When the sword is once again wielded in battle by a descendant of Slytherin, Slytherin himself will return, and he and his descendant will join together to wreak havoc and terror on the wizarding world.
Remus. He turned back to the other cell, where the werewolf lay. It bared its teeth at him as he approached, its dark eyes wide with ferocity or pain or some combination of the two.
'Are you going to kill him, finally?' drawled the demon at Sirius' back.
