Harry apparated them to the cave above Hogsmede and the pair quickly fell into habit, Hermione started work on their protective enchantments whilst Harry headed inside to make the space comfortable. It was a familiar routine by now and one that she was perfectly comfortable performing, so she was surprised when she felt Grindelwald beginning to weave his own magic around hers, modifying her wards. There was something unusual about the way his changes settled, as if they were drawing power from a non-magical substance. She opened her eyes to see him placing his spiders along the perimeter of the camp.

'It would surprise you how many powerful wizards can't deal with the unexpected.' He explained, placing the last of his spiders right next to where she stood. He gave her that strange, one sided smile as he straightened and disappeared after Harry into the cave.

Harry had done a brilliant job inside, he had pulled out a couple of jars of bluebell flames and arranged them to light the space. Heating charms were slowly working their magic on three bowls of soup which sat on a roughly transfigured table – leaves still sprouted over the surface, so she assumed it had once been a twig.

Gellert conjured three squishy armchairs and cast a warming charm over them. Before he sat, he patted the cushion over thoroughly and withdrew several metal pins.

'Albus was brilliant at this spell, mine always have pins in.' He grumbled, tossing the offending metal scraps away.

'You're focusing too hard on creating a chair, the emphasis needs to be on sitting in the chair.' Hermione informed him as she carried the bowls of soup over.

'Blimey Hermione, you should take over from McGonagall.' Harry said as he emerged from her beaded bag with the Marauder's Map. He spread the map out over the table with one hand as he picked up his soup with the other. Hermione hastily summoned the needles out of his seat as he sat down, before doing the same to her own. Grindelwald watched on curiously as Harry muttered the password and the map began to appear before them.

It hadn't modified, Hermione noticed, to accommodate for the damage to the castle during the battle. The inky halls remained intact, the entrance hall doored, the statues in place, only the change in names signalled that something was amiss.

The dungeons were full, that became immediately clear, although they recognised none of the names. The corridors were patrolled by the Carrows and the Malfoys, Voldemort was ensconced in the Headmaster's office.

'The anti-apparition wards are back up.' Hermione informed them, pointing out Nott hurrying up the grounds from the gates.

'Looks like Pettigrew told You-Know-Who about all the passages, so they're probably warded too.' Harry added as Lucius Malfoy paused his patrolling to check inside the blocked passage behind the portrait of Merlin. 'They're not very up to date at least, Fred said that passage has been blocked for years.'

'The room of requirement isn't on here.' Hermione pointed to the 7th floor corridor.

'It might not exist anymore, Crabbe cast Feindfyre in there, remember?'

'Feindfyre doesn't damage stone.' Grindelwald commented casually, 'although the room will probably be full of Ashwinders.'

'We need to check there, we'll go through the Hog's Head passage.' Harry decided, 'then we need to free the prisoners, we can't just leave them.' Grindelwald rolled his eyes and mumbled something unflattering about heroes but as he worded no complaint, the plan was decided for the next day.

Harry packed the map away and left the cave to do the dishes, Hermione finally decided to broach the real reason she had released Grindelwald.

'Are you familiar with prophesies?' She asked him, from his derisive snort she assumed that like her and every other intelligent wizard, he didn't hold much stock in prophesies.

'I am a seer, Miss Granger. I am intimately familiar with prophesies.' He informed her, which was enough to make her relieved she hadn't expressed her views. It also completely sidetracked her as she bombarded him with questions. She'd never spoken to a genuine seer before about divination (which was a subject he did find stupid; either you have the talent or do not.) He explained that tea leaves were a lost cause, most of his visions were entirely unprompted and came in dreams, although a dream diary was a waste of time as a vision was very difficult to mistake for a regular dream. Hermione listened with rapt attention as he described the vision that he had seen of the trenches in World War One that had rallied so many to his cause and how his vision of the Second World War had been the trigger that began his campaign.

She was finally brought back to the present when he asked why she was interested in prophesies. She then described how Harry was the subject of a prophesy and how he was the only one that could kill You-Know-Who. She related the exact wording to the Seer, who laughed at the foolishness of a Dark Lord who chased prophesies.

Then came the complication.

'Have you heard of a horcrux?' Hermione asked him, whispering the word as if saying it quietly would lessen the evilness of the subject.

'I have heard of them. I assume Vold-You-Know-Who has made one.'

'He made seven.' She informed him, at which point Grindelwald made an appreciative noise.

'Seven is a powerful magical number. I can see the appeal, although if he had done enough research he would have realised that horcruxes only prevent death, not aging.'

'He killed someone to extend his own life.' Hermione said, outraged that Grindelwald was only seeing the personal benefits and disadvantages.

'No, he killed someone to extend his own existence. With access to the right information he would have realised he could still age and die naturally, then only get a new body if his followers loved him enough to create the potion. Few followers love a leader that tortures them.' He corrected, entirely missing Hermione's point. Remembering that she was talking to the man that killed an entire town of muggles to create inferi, she gave up, moving on to the more relevant matters at hand.

'We've destroyed five of the seven; Slytherin's locket, his family ring, Hufflepuff's cup, Ravenclaw's diadem, his school diary. His snake is one, and the last...'

'Is Mr. Potter' Grindelwald finished. 'You can't destroy the horcrux without killing him, you can't kill You-Know-Who if you kill . I assume having Potter reduce You-Know-Who to a wraith, then killing Potter is not a viable option?' Hermione's expression let him know that was certainly not an options, and she prayed that Harry wasn't close enough to hear that solution.

'I was considering transfer.' She suggested. 'I only have basic knowledge, of course, that's why we needed your help.'

Grindelwald was silent for several long moments as he considered the problem.

'Theoretically it would be possible. Creating a horcrux is split into three separate stages; committing murder only damages the soul temporarily, so the first stage is to allow for a full and permanent tear. The second stage is to create the tear by murdering someone. The final stage is to transfer the torn section into the new object and link it to its new host. I have only read about the process in passing but I have a text which details the process in Nurmengard.' Hermione was nodding but a cold feeling was working its way into her gut. She felt dirty even knowing the theory of this. Grindelwald didn't seem to notice, wrapped up in the thrill of an academic challenge as he described the simple process of detaching an entire soul from its host, and potential ways to isolate it to only remove the horcrux.

When she could take the details no longer, and feeling as though she knew far too much, Hermione finally interrupted.

'I'm sorry, Mr. Grindelwald...' He finally looked up from the runic diagrams he'd drawn onto the table and noticed for the first time how pale she was. He jumped up, apologising profusely as he summoned hot cocoa from the beaded bag and made her a hot chocolate.

'I saw what I would become when I was too young to understand that it was not normal. I'm sure you're aware that I was expelled from Durmstrang for practicing blood magic when I was sixteen. Albus used to get sick sometimes, when he caught me practicing, he used to say that he felt tainted afterwards. He claimed that chocolate was the cure for all dark magic.' He handed over the steaming mug and took his seat again.

'I think I understand. I feel like I know too much.' She took a sip of the chocolate, which burned its way down to her stomach. 'I read about your friendship with Dumbledore.' She told him, which seemed to surprise the Dark Wizard.

'He was usually very private, I was unaware that he'd ever even admitted that we were associated.'

'Rita Skeeter published an autobiography. I think she forced Bathilda Bagshot into taking veritaserum.'

'Is this woman dead yet?' He asked in such a flat tone that at first Hermione thought that he was joking. Then she realised that he was fingering his wand as if he was considering which spell in his arsenal to inflict on her. 'Aunt Bathilda was always good to me.'

'I find a mason jar is usually enough of a threat.' Which launched them into a conversation on animagi, which Harry soon returned to join in on.