Fred and George arrived the following morning.
They came with the specific energy of people who had heard something interesting and had waited as long as they were capable of waiting, which was approximately sixteen hours.
Fred came through the door, looked at Sirius, and said: 'You're Padfoot.'
Sirius looked at them. 'Where did you hear that name?'
'We have our sources,' George said.
'You have a map and you overheard my conversation with Moony as you entered the floo,' Sirius said.
The specific quality of attention that entered Fred and George in that moment was one Ron had seen before — the attention of people who had just discovered that the person across from them knew something they didn't expect the person to know, and who were simultaneously pleased and recalibrating. They sat down on the floor near the fire, which was where Fred and George always sat when a conversation was about to become interesting, and looked at Sirius with the expression they used when they were assessing the probability of obtaining information.
'The map,' Fred said carefully, 'is a device of considerable sophistication.'
'I know,' Sirius said. 'I helped make it.'
The silence that followed had the quality of a pause before something reorganized itself.
Ron sat back in his chair and took a photograph of Sirius's face, and Fred and George's faces, and did not say anything because there was nothing to add and everything to observe.
What followed was two hours. Sirius talked about the map — how it had been built, what it had taken, the specific magic of the Animagus tracking and the Homonculous Charm and the way the four of them had argued about the naming scheme for months before settling on the one that was there. Lupin filled in the parts Sirius underplayed, which were the parts that required the most skill and which Sirius attributed to collective effort with the reflexive modesty of someone who had always been better than he admitted. Fred and George asked questions with the focused intelligence of people who had been using a piece of magic for two years without fully understanding it and were now getting the architecture for the first time.
'The notes,' Fred said, at some point in the second hour. 'You had working notes. For the construction.'
'Somewhere,' Sirius said. 'In storage. I haven't gone through everything from — before.'
'If you find them,' George said, 'we would be very interested in reviewing them. Academically.'
'For research purposes,' Fred agreed.
'You want to build a better one,' Sirius said.
Fred and George said nothing, which was confirmation.
Sirius looked at Lupin. Lupin made a gesture that communicated something between 'this is your decision' and 'I am mildly interested in what happens next.'
'If I find the notes,' Sirius said, 'I'll consider it. In exchange for the map itself now. It should be Harry's.'
The negotiation that followed took approximately four minutes and produced a handshake. Ron photographed the handshake.
After Fred and George had gone — with the specific energized quality of people who had arrived for a conversation and were leaving with a project — Ron waited until Sirius and Lupin were in the kitchen, and said, quietly, so only Harry could hear:
'The map shows everyone in the castle. By name. Every person, every room, every passage.'
Harry looked at him.
'That's going to be useful,' Ron said.
Harry was quiet for a moment, turning this over. Then he nodded, with the specific quality he had developed over the autumn — the one that did not ask how Ron knew things, just filed the information and used it.
'Yes,' Harry said. 'It is.'