The second task preparation ran parallel to the combat training, which meant January had the density of a month carrying two full agendas simultaneously.
He had found the Gillyweed potion recipe in the Black library over the summer — not the standard Gillyweed consumption method, which was simply eating the raw plant, but a prepared potion version that Neville had confirmed existed in a Herbology text he had read in third year. The potion version had one significant advantage over the raw plant: a controlled duration. Raw Gillyweed was unpredictable — the transformation could last anywhere from an hour to two depending on the quality of the plant and the magical capacity of the person consuming it. The potion standardised this to exactly sixty minutes from the moment of full transformation.
'Sixty minutes,' Harry said, looking at the recipe.
'From full transformation,' Ron confirmed. 'Not from drinking it. The transformation takes approximately two minutes. So fifty-eight usable minutes in the water.'
'And the task is an hour.'
'Yes. Which means you need to be efficient.' He looked at the recipe. 'The brewing time is four hours. The ingredients are straightforward — Neville can source the Gillyweed through the greenhouses, the rest is standard potions stock. I'll walk you through the process but you're brewing it yourself.'
Harry looked at him.
'I can brew it for you,' Ron said. 'My potion would probably be more consistent. But the task is yours, Harry. In the final tasks and in the things that come after them, there will be moments when no one is there to do it for you. Better to learn to do it yourself now, when there's time to get it wrong and try again.'
Harry held the recipe for a moment. 'How many attempts do I get?'
'As many as the schedule allows,' Ron said. 'February gives us three weeks before the task. One brew per week. Three attempts.'
Harry nodded. Something in his expression had the quality it had when he received a framework and was already beginning to work within it. 'Okay,' he said. 'Show me how to start.'
They set up in the Room of Requirements, which produced a potions station with the specific professional quality of a space that understood what it was being used for. Ron walked him through the preparation — the Gillyweed first, which needed to be processed in a specific sequence, then the stabilising base, then the thermal management that the recipe required and which was the technically demanding part of the brew.
Neville, who had joined them for this session, watched with the specific focused attention he brought to Herbology-adjacent work. 'The Gillyweed needs to be fresh,' he said. 'No more than three days from harvest. If it's been dried the potency drops significantly.'
'Can you source fresh?' Ron asked.
'The greenhouses have some,' Neville said. 'Professor Sprout won't notice three stems going missing if I time it right.'
'Don't take it without asking,' Ron said.
Neville looked at him.
'Ask her. Tell her it's for a project. She'll say yes.'
Neville considered this with the expression of someone discovering that the honest approach was also available and had simply not been the first option he'd reached for. 'Right,' he said. 'I'll ask.'
Harry's first brew took six hours and produced something Ron assessed as approximately seventy percent correct — functional, probably, but not consistent. He told Harry this without softening it. Harry noted the specific points where the thermal management had drifted and scheduled the second attempt for the following week.
The first attempt was exactly what it was supposed to be.
The swimming presented a problem he had not fully anticipated.
He had known, from Ron's memories, that Harry Potter's upbringing had not included swimming lessons. This had seemed, in the abstract, like a gap that could be addressed. In practice, the specific challenge of teaching someone to swim who had no physical memory of being in water — no instinct for how water worked against the body, no unconscious knowledge of how to float — was more demanding than he had expected.
The lake was cold. January in Scotland and the Black Lake were not natural companions, and the Gillyweed transformation would manage Harry's breathing but not the temperature, and the temperature needed managing before the task.
He solved this in two parts.
First, he warmed a section of the lake. This required a sustained Warming Charm across a roughly fifteen-foot radius of water, which he held for two hours on the first Sunday afternoon — the specific sustained-output cost he had been documenting and managing since second year, higher than he would have preferred but within what he could afford. He stood on the bank with his wand extended and let the warmth move through the water and thought about the training curriculum and the second task and the things coming after both.
The second part was simpler: he went in first.
He was a competent swimmer — his previous life had included a year near the coast and a deliberate decision in his mid-twenties to learn properly. He had the muscle memory. He went into the warmed section of the lake and demonstrated what Harry needed to know, starting with the basics that were not basic at all to someone without them: how to float, how to read the water's resistance, how to move with it rather than against it.
Harry stood at the bank with the expression of someone facing something they had decided they were going to do and were still determining how.
'It holds you,' Ron said, from the water. 'That's the thing that doesn't feel true until you're in it. You don't have to fight it.'
Harry came in.
The first session was thirty minutes and Harry spent most of it working out what the water wanted from him, which was not the same as fighting it but was adjacent. By the end he could float without effort, which was the foundational thing and worth the thirty minutes entirely.
The others had come along, because the others generally came along when there was something happening that involved Harry's preparation — and also, Ron suspected, because a warmed section of the Black Lake in January was not an opportunity most people encountered.
He had not fully thought through the swimsuits.
In principle there was nothing to think through. They were four fourteen-year-olds and one fifteen-year-old doing a practical training exercise in controlled conditions in January. The swimsuits were functional. Everything was entirely appropriate.
In practice he found himself very carefully looking at the water.
Hermione came in after Harry, without drama, and swam with the competent ease of someone who had taken the relevant lessons at the relevant age and had retained them. She did not look at Ron. He did not look at her. They were both looking very determinedly at Harry, who was attempting a proper stroke and succeeding approximately sixty percent of the time.
Ginny, in the water beside Harry, was demonstrating something with her arms and saying something Ron couldn't hear from where he was.
Neville had waded in to his waist and appeared to be considering his options.
Luna was floating on her back with her eyes closed and the specific quality of someone who had decided that floating on her back in a magically warmed lake in January was simply what was happening and had no objections to it.
Ron swam a lap of the warmed section and came back to where Hermione was treading water and did not look at the way the water moved over her shoulders and looked instead at Harry, who had abandoned the stroke and was doing something more improvisational that was nonetheless working.
'He's getting it,' Hermione said.
'Yes,' Ron said. He was looking at Harry.
A pause.
'Ron,' Hermione said.
'Yes,' he said.
'You can look at me,' she said, with the specific precision of someone who had noticed something and had decided to name it rather than let it accumulate. 'We have been together for almost a year and you are being extremely strange about a swimsuit.'
He looked at her.
She looked back with the expression that was not quite amusement but was adjacent to it — the specific look she had when she had caught him at something and was choosing to find it endearing rather than ridiculous.
'You're very,' he started, and then did not finish the sentence, because all of the available endings were either accurate and embarrassing or inaccurate, and he had a policy about inaccuracy.
'Thank you,' she said, which covered all of the available endings simultaneously, and pushed off into a backstroke that was technically perfect in the way that everything Hermione did technically was, and he watched her go and thought: fifteen is a very specific kind of difficult.
Harry, from four feet away, said: 'Are you two going to be like this all session?'
'We are training,' Ron said, with dignity.
'Right,' Harry said, entirely without conviction, and went back to his stroke.