He found Ginny at the dueling posts at half past eight on the evening before the task.
She was working through a sequence he recognized from the third week of training — the combined footwork and non-verbal casting drill that Harry had finally cracked in the pressure sessions, the one that required the body to have absorbed the grammar well enough to run it without the head managing it. Ginny had absorbed it faster than Harry and was now doing what she always did with things she had absorbed: pushing the edges, finding out what happened when she ran it at a pace slightly faster than the drill specified.
He watched her work through it twice before she registered him.
'Second task is tomorrow,' she said, cancelling the non-verbal and turning.
'Yes,' he said. 'I need to tell you something about tonight.'
She looked at him with the quality she had when she was assessing the register of what was coming — not alarm, just calibration. 'Alright.'
'I've had a working theory since the Yule Ball about what Harry would be retrieving from the lake,' he said. 'Based on the clue and the pattern of the Tournament and the most logical way to construct the task.' He paused. 'My theory is that it's someone he'd miss. Someone who matters to him.'
Ginny held his gaze. Her expression didn't move. Not surprise.
'You think it's me,' she said.
'I think it's possible,' he said. 'I don't know for certain. I won't know for certain until tomorrow morning when the hostages are taken — and by then there's nothing I can do about it that wouldn't interfere with the task itself.' He looked at her steadily. 'What I can do tonight is place a tracking charm on you. A passive one — it won't activate unless I choose to activate it, and it won't affect you in any way. If you do end up in the lake it will give me a rough bearing on your position.'
'Why a rough bearing,' she said. 'Why not exact?'
'Because I'm not casting it into the lake,' he said. 'I'm casting it on you, now, in air. The accuracy across depth and distance in moving water is limited. I'll know the general area. Not the metre.'
She absorbed this. 'And if it's not me?'
'The charm sits inert,' he said. 'You won't notice it. It disappears by itself after twenty-four hours.'
She looked at him for a moment. 'You've been planning for this since December and you're telling me the night before.'
'I'm telling you before it happens,' he said. 'I'm not telling you in advance because knowing in advance changes things — how you sleep, how you feel tomorrow morning, whether you say something to Harry or Mum that shifts the day in ways I can't predict.' He paused. 'I wanted you to know. I didn't want you to know for weeks.'
Ginny was quiet for a moment. Then she said: 'That's a very specific kind of considerate.'
'It's the only kind I know how to do,' he said.
She looked at him — the specific look she had for him when she was seeing the shape of what he was rather than just the immediate surface of it. Then she held out her arm. 'Do it,' she said.
He cast the tracking charm. Passive, light, the specific quality of something that would wait until he asked it to speak. It settled on her like nothing at all, which was the correct outcome.
'If I end up in the lake,' Ginny said, 'I want a full account afterward of what it looked like from the bank.'
'Done,' he said.
She picked up her wand again and went back to the drill, slightly faster this time, and he went back to the castle and the third brew of the Gillyweed potion, which Harry had completed that afternoon with the specific clean confidence of someone who had done the same thing three times and understood it now rather than just executing it.
He knew at seven fifteen on the day of the task.
He was at breakfast when he felt the tracking charm activate — not dramatically, not with any sensation he would have noticed if he hadn't been waiting for it, but with the specific quiet quality of a charm reporting in the way he had built it to report: a directional awareness, faint and steady, pointing toward the lake.
Ginny was not at breakfast.
He looked at Harry, who was eating with the focused quiet of someone managing their nerves by attending to ordinary things, and thought: he doesn't know yet either. He'll find out at the lake.
He caught Hermione's eye across the table.
She had noticed Ginny's absence. She looked at Ron with the specific quality of someone who had been building toward a conclusion and had just received the last piece. He gave her the fractional nod that confirmed it.
She closed her eyes for a moment. Then she opened them and went back to her breakfast with the specific quality of someone who had received difficult information and had decided to be functional anyway.
Harry looked up from his plate and looked at the empty seat where Ginny usually sat.
The expression that moved through his face lasted approximately two seconds and then was managed away, because Harry had been managing things in his expression since he was old enough to understand that showing things at the Dursleys had costs. But the two seconds were real, and Ron saw them, and filed them alongside everything else he knew about Harry Potter and the specific weight of the things he carried.
He reached over and put his hand briefly on Harry's arm. Not words. There were no useful words for this particular moment.
Harry looked at him.
'She's safe,' Ron said, quietly. 'The hostages are protected for the duration of the task. That's the design. She's fine.'
Harry held his gaze for a moment. Then he nodded once and went back to his eggs, and Ron thought: he believes me. Not because I've proved it. Because we've built the kind of thing where he believes me. That has a cost to it. It also has a value that is not reducible to the cost.