Harry crumpled up the piece of parchment entitled The Big Book of Future Tournament Tasks and lit it on fire with his wand. ‘Best there’s no evidence.’

‘Nobody else can see it, it’s down here.’

‘Fawkes got down here.’

Salazar rolled his eyes. ‘I’ll explain when you know more magic.’ He reeled his serpent in and coiled it round his arm. ‘Did you ever deduce the meaning of the message you just burnt?’

'I can guess.’

'Did you guess?'

'There were dragons, the tiny model dragon that was used to select them bit me, and Katie Bell, one of my Gryffindor house-mates approached me after the match.'

'The small one bites.' Salazar cackled. 'Why so ambiguous?'

'If I’d been forewarned too specifically the model would not have had the chance to bite me and I would not have been motivated to take it into the arena with me.' Harry shrugged. ‘If I hadn't told myself at all, I probably would’ve ignored it and missed how useful it ended up being. It had to be just right.'

'Very astute of you. It explains why you were grinning to yourself when you wrote the note, too.'

'I've never played a prank on myself from the future before,' Harry said. 'I found the concept quite entertaining.'

'So did Godric,’ Salazar muttered. 'Only he didn't have the decency to carry out his childish activities on himself.'

'What about this Katie Bell?' Salazar asked. ‘You’ve never mentioned her before.’

'I think she’d’ve been angry with me if I’d ignored her like I nearly did.’

'Important, is she?'

Harry shrugged. ‘She's a friend, I suppose. A teammate, really, but she stuck by me and tried to help.'

'Don't want her changing her mind and undoing everything she did.' Salazar nodded. ‘An equal, maybe?’

The snake mimicked the motion and stuck its tongue out alongside the inside of Salazar’s palm.

Salazar fidgeted, itching at his palm. ‘Wretched reptile. I wish I’d decided to make you part of the design of the frame of this painting instead of putting you in here with me. You can’t even talk!’

‘Why not?’

‘The snake has to be smart enough. While I enchanted the painting to be a sort of copy of myself, this useless scaly worm is just paint and canvas charmed to act like a snake.’ Salazar unwound it off his arm and draped it over his shoulders. ‘Grab that book off the shelves behind you.’

Harry stared at the hundred or so books on the shelf. ‘Which book? The small one?’ He squinted at the title. ‘A Thousand and One Snake Puns?’

Salazar coughed and turned a little pink in the face. ‘Not that one. My one. Writing in the Elixir of Life.’

Harry ran his finger along the titles. ‘This is the biggest book in the library.’

‘Second biggest.’ Salazar pointed his wand into the far corner. ‘Rowena wrote a treatise called Arithmantic Principles in Potions that's ten thousand words longer.’

‘Well, I’m not reading that.’

Salazar chuckled. ‘I didn’t either. Rowena knows her stuff, but her writing was always very matter-of-fact and dry.’

‘Not like Salazar Slytherin’s bestseller, A Thousand and One Snake Puns. Don’t think I didn’t see the name of the author.’ Harry caught a fair few choice words in parseltongue as he dragged the ancient, leather-covered, heavy tome.

‘Just take me and the books outside.’

Harry levitated a stack of tomes off the desk and lifted the portrait off the wall to carry Salazar out into the main chamber.

'Now I can finally teach you about the things I was exceptional at!’ Salazar’s wand spurted silver and green sparks over the head of his serpent. ‘Naturally, as my heir, you’ll be exceptional at them, too.’

‘Naturally…’ Harry leant the portrait against the foot of one of the serpent effigies and took a seat on the floor in front of the painting. ‘So?’

'Where to begin?' Salazar muttered, rubbing his palms together. ‘Where to begin?’

'The basics?' Harry suggested.

Salazar’s face fell. 'Fine.' He sighed. 'It will take an age to get to the exciting things, but I suppose it's better than you accidentally destroying the chamber… or yourself.’

Harry groaned. ‘This is going to be a really dry conversation, isn’t it?’

‘Blood magic is any magic that uses blood as a medium or tether, but due to its potency and complexity, it’s mostly just used for sacrificial and ritual magic,' Salazar said. 'The only real rule for sacrificial magic, is that whatever you sacrifice must be equal to whatever you are trying to achieve.'

'That's it?'

'Of course that isn't it! Sacrificial magic is a very subtle, delicate thing. It requires a full, true understanding of magic and self. You cannot really sacrifice something when you do not know its value, nor can you attain a result you do not already understand the implications of.'

'What can I actually do with it?'

'Anything and everything,' Salazar said. 'Parselmagic, the magic at the root of parseltongue, is merely an example of complex blood magic, that is to say sacrificial magic in which blood was used as a medium and as the anchor of the magic. This chamber, the thoughts of sufficiently intelligent serpents, and our magic, are all bound to the blood that flows in my veins and thus in yours. It’s perhaps my finest creation. The ability to speak to animals was once more common and applied to more than just snakes, but over time it was lost. The last witch recorded as being capable of speaking to animals died half a millennia before I was born. I attempted, originally through other means, but eventually through blood magic, to recreate part of what was lost. I was not prepared to sacrifice anything more than I did, so my piece of magic only responds to serpents as they are easily summoned.'

'What did you have to sacrifice?'

'Something that was of equal value to me. Someone, to be precise.'

Someone?! Harry felt ice form in his veins.

He stared at the painting, cold horror curdling in his gut. 'You sacrificed a person!?’

'She was dying already. We sacrificed the little time we had left together, much as it meant to us, to create something that would aid and set apart our children and their descendants for as long as they survived.'

'Sorry. I should’ve known better than to assume.'

'Yes you should have,’ Salazar snapped. 'You do not understand the magnitude of the sacrifice. Even I didn’t until after I’d done it. My daughter and I searched for many years for an artefact rumoured to be able to cheat the laws of death and enable us to speak with her again. I never found it. I became too old to hunt for it and was forced to give up, but my daughter had not before I died. It is possible she was successful, but I would not know either way. That sacrifice defined the rest of the lives of myself and my daughter in one way, then the rest of our descendants in another. If you take anything from that, let it be the realisation of the kind of effect blood magic can have on your life.'

'How does it work?' Harry asked.

'Blood is the most potent magical medium — personal and puissant. Blood magic makes use of it as a conduit through which to perform otherwise impossible feats.'

Something impossible?

Harry traced a finger down his scar. 'Like surviving the Killing Curse, perhaps?'

'There are very few pieces of magic capable of achieving that.’ Salazar stroked his chin. 'The Killing Curse is not a simple spell. It is a derivation of one of the only other fields as powerful and complex. Blood magic could be used, but it would come at the cost of the caster's life, or more, rendering the protection irrelevant.'

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'But you could cast it to protect someone who shared your blood?'

'Perhaps... It would not be easy, but it’s a fascinating idea. I think to make a whole bloodline immune to such a powerful curse would cost more than anyone has to give.'

'I survived it,' Harry said. 'When I was a baby, Voldemort came to kill me. He managed to murder my parents, but his intended final victim reflected his curse back onto him.'

'That could well be blood magic,' Salazar said. ‘Perhaps they only afforded you that protection. It would reduce the sacrifice to a level that would be possible to make, though it would have still been very dear indeed.'

‘They did die.’

Salazar’s brow creased and he stroked the head of the snake that curled around his shoulders. ‘I would guess they carried out a blood magic based piece of sacrificial magic that would come into effect should they both die to keep you safe. Your safety from this attacker would be the goal and it would certainly constitute a sacrifice dear enough to protect you.'

'It lasted at least as long until I was eleven,' Harry replied. 'When Voldemort tried to harm me in my first year here, he burnt at my touch.'

'It may still be in effect now. Your parents sacrificed their lives and every moment they would have spent with their child, there is little of greater value to a parent.'

'I'd rather not need it.’

'You will not,' Salazar said. ‘But it is a powerful advantage while it lasts. The magic will protect you in any way it can as long as it lingers in your blood. Still, it goes without saying that you should avoid lethal spells, especially the Killing Curse.'

'Why especially? Dead is dead.'

'Most lethal spells are really no different from other curses in that they just cause something to affect you. In the case of most lethal spells the effect is what truly kills you and effects like that can usually be prevented in numerous ways. The Killing Curse is derived from soul magic. It literally tears your soul from your body. The curse kills you outright rather than causing or creating something to do so.'

'Soul magic?'

'Not something I ever more than dabbled in the practice of. It’s the equal of blood magic in some ways, but far more abstract in its concept and very dangerous because of it. I know of few uses for soul magic worth their cost. The Killing Curse is one of the few soul magic spells that has no permanent effect. Using it causes the soul to fracture, but over time, in the right conditions, a soul can heal. If you are interested, there is a very old Egyptian book in my study. It's hardly a guide to the field, but the wizard referenced in it, Seth, is attributed with the first use of the Killing Curse. He was likely its creator.'

'The name sounds familiar.’

'You might have heard it in the muggle world. The muggles of Egypt used to us that name for their God of murder. Whether there's a connection is unclear.'

All things considered, it seems likely.

'Did you bring all the other books I recommended to you before?' Salazar asked.

'Yes.' Harry named them one after the other, descending down the stack. ‘See?’

'The Secrets of the Darkest Arts?'

'I didn't mean to bring that.' Harry stared at the weathered book and the sheafs of parchment wedged within the pages. 'I must’ve stacked the other books on top of it in the study.'

'It probably has something useful in it. Blood magic is powerful magic and powerful magic has always been used in questionable ways. The element of sacrifice doesn't help its reputation any.'

Harry studied the neat, flowing script on the parchment that stuck out of its pages. Riddle’s handwriting.

'I'll read it last,' he said.

'Take them to the Room of Requirement after this tournament meeting you have to attend,' Salazar suggested. 'Just make sure you aren't seen reading them and bring them back to the study afterward. Most of those books were old and valuable when I acquired them; they'll be worth a fortune now.'

Harry cast a quick time-checking spell only to find that it would soon be time for the meeting. How does he even know what the time is?

'There's nothing else I can teach you until you've read those and understood the two principles of blood magic and their applications. It isn't a pure subject like transfiguration, but it can be used to augment or create wards, enchantments, and many other such areas.'

Salazar groaned and screwed up his face. 'I just quoted Godric. He used to go on and on about how blood magic wasn't really a field in its own right. Oh I bet he’s giggling away in the afterlife right now, the overgrown child.'

Harry carried the portrait back, shrank the books and stashed them in his pocket, then swiped his golden egg off the study desk.

Salazar’s grumbling followed him all the way up the stairs to Myrtle’s bathroom.

He’s probably still going now. Harry hurried toward the classroom for his tournament meeting. As long as he’s not still going when I get back.

'All our champions are here!' Bagman swung his legs off the edge of a desk, the black and yellow robes of his old beater’s shirt drawing tight over his belly.

Mr Crouch frowned and tapped his pocket watch. 'The first task is over. You have each obtained the golden egg your dragons were guarding and achieved a score for your methods.'

'Some of which were spectacular.' Bagman stuck both his thumbs up at Harry and grinned.

'The egg is your clue for the second task.’ Mr Crouch paid Bagman no heed. ‘Solve it.'

Harry examined his egg, turning it over in his hands. I'll have to try opening it. It’s an egg, so it makes sense the clue would be inside.

Cedric bounced his egg in his hands and Fleur ran her wand tip over hers.

Krum scowled and gave his a shake. ‘Well, it does not rattle, so at least it’s not more broom polish.’

Harry snorted. ‘If it sprouts wings and flies off, you can borrow my Firebolt.’

Krum grinned and gave Harry a sharp-eyed once over. ‘You have Firebolt? Seeker, yes?’

'Well, unless any of you have questions this meeting is concluded.' Mr Crouch slipped his pocket watch back away and strode toward the door.

'Harry.' Bagman caught his arm at the door. 'If you want a hand with the egg just give me a shout,' he whispered. He walked away with a wink.

Crouch cut him off with a stern expression and the two held a furious, muttered argument on one side of the corridor.

Harry cradled his egg beneath his arm and set off in the direction of the Room of Requirement.

‘Hey Harry.’ Ginny sidled into his path.

'Ginny…'

‘Er…’

'You stopped me,' he said.

'I know.' She flushed. 'I wanted to say sorry.'

'A lot of people have been from what I've heard.'

'A lot of people didn't want to try and stand up to Angelina and all the seventh and sixth years.' Ginny squirmed. ‘Sorry.’

'Angelina’s having a change of heart, apparently.’

Ginny’s eyes narrowed and her jaw tightened. 'Katie said that, did she?'

Harry raised an eyebrow. 'She did.’

'I didn't turn my back on you. I just didn't want to suddenly act all close with you, because — well, because I was afraid you'd think I was just trying to get close to you.'

'You should have done. I probably would’ve noticed, but I wouldn't have minded all that much.'

'It's too late, isn't it.’

'Sorry. If it helps, I'll accept your apology.'

She smiled. 'I'd like that. I was hoping to be someone better this year, not just Ron's little sister who got into trouble and needed rescuing.'

'You succeeded.’ Harry shot her a grin. 'I haven't seen you stick your elbow in a butter dish in years.'

Ginny went bright red and covered her face with her hand. 'Oh no. You saw that.’

'I tried not to laugh.' He let the smile slide off his face. 'I'm not the same boy who rushed down to the Chamber of Secrets after a basilisk to save you anymore, Ginny.'

I never was.

'Hermione said you'd changed.'

'She's right.’ A little ice crept into his tone.

She winced. 'Touchy subject.’

'You wouldn’t be fond of someone who broke your wand, either. I heard what happened to Ron.'

'He was being an idiot.' Ginny scowled. 'He still is.'

'Still?'

I’ve not seen him for a while, actually.

She shook her head, sending her long red ponytail swaying behind her. 'He and Hermione have some ridiculous theory that something happened to you at the World Cup. They think you were hit by some dark curse and that it affected you in the head.'

Harry laughed. 'Does anyone actually believe that?'

'Seamus and Dean, but a lot of the house is just sick of the whole thing now. Most are just avoiding anyone involved or waiting to see who turns out to be right. Neville still hangs around Ron and everyone, but it's because he hasn't got the courage to go make other friends.'

Harry smiled. Now the shoe’s on the other foot. Serves them right.

'They do deserve it.’

The Great Hall started to fill with people as lunch drew near and Harry began to shift restlessly from on foot to the other. ‘Was there something else?’

Ginny shuffled her feet. 'I was hoping you'd come eat lunch with us.’

‘Us?' Harry frowned. ‘A lot of your friends might not be so keen about that.’

'Me, the twins, a few others.’ Her lips thinned. ‘Katie will be there.’

'I have to go play with this thing.' Harry tapped the top of his golden egg.

A clear, ringing sound came from his clue.

'I see.’ Ginny’s brow wrinkled and she sighed. ‘Well, I hope the second task goes as well as the first.’

It has to go better. I’m not going to beat Krum or that French girl if it doesn’t.

Harry slipped through the Great Hall and made his way up to the seventh floor and the hidden room opposite the tapestry of tap dancing trolls.

I need somewhere to solve the clue of the egg. He focused on his desire and waited until a door appeared.

A simple, plain room lay beyond. The carved half-fish, half-human forms of some creatures wielding tridents swam in excited shoals over a stone bench, scattering when he approached to sit. A small bubbling pool commanded the room’s centre.

Not quite what I expected. Harry glanced round the room and down into the clear water. Clearly this room has some nuances I’ve not quite grasped.

He sat down and turned the egg over in his hands, looking for a catch or clasp. Harry tapped it with his wand, and it split in half.

A piercing shriek tore through the air.

Harry slammed the egg shut. Some clue that is!

He took a deep breath. ‘Stupid egg. I hate loud noises, especially unexpected ones.’

The mermaids on the bench gestured at him, waving their tridents in the air.

Blood magic first. It’s ages until the next task. Harry dropped the egg on the floor and swung his foot at it.

The egg rolled across the floor and teetered on the edge of the bubbling pool. Harry ignored it and pulled out his stack of books.