Hermione quit Muggle Studies on Monday of the third week.
She had been considering it since November — he knew this because she had mentioned it once, in October, in the specific way she mentioned things she was thinking about, which was to say it once and then not say it again until she had reached a conclusion. The conclusion had apparently arrived over the weekend.
She told McGonagall on Monday morning and handed back the Time Turner on Monday afternoon, which she did in McGonagall's office with the quality of someone returning something borrowed, correctly and on time. He knew about the Time Turner. He had known about it since September, when he had first noticed the particular way she occasionally arrived at classes looking as though she had come from somewhere else immediately before. He had not mentioned that he knew.
What he had not known was what she would do with the time.
On Tuesday she appeared at the Thursday Patronus session with Lupin with the specific expression of someone who had arranged something and was presenting the arrangement as a fact rather than a request.
'I'd like to join,' she said to Lupin.
Lupin looked at her. Then at Ron. Then back at her.
Lupin considered this with the quality he brought to requests that were technically outside his remit and practically very sensible.
'Thursday evenings,' he said. 'Both of you. We'll begin from the beginning for you and continue the message work for Ron.'
'Thank you,' Hermione said, with the precision of someone who had expected this outcome and was confirming it.
After Lupin left the corridor she looked at Ron.
'You knew I was going to ask,' she said.
'I thought you might,' he said. 'The time freed up and you don't leave time empty.'
She looked at him. 'You could have suggested it.'
'It worked better when you decided it yourself,' he said.
She was quiet for a moment with the quality of someone who was going to argue with this and had decided not to, because he was not wrong.
'Fine,' she said.
He smiled. She saw him smile and her expression did something that was not quite suppressing a smile of her own and was not quite failing to suppress it. They walked back to the common room and he thought about the foot under the table and the yes in the early morning common room and the card on the shelf between books, and found that the collection of small things had become, without announcement, something he carried with him.