One of them was always here, what with Verity manning the new shop in Hogsmeade. George was off with Lee again, which left Fred at the shop. Middle of the week and end of the day, though, it was nearly deserted and he was at the counter hunched over a piece of parchment with incoherent drawings on it, symbols and runes that were part of the language he and George had created for their experiments and charms.
This one was quite a bit more important than any of their current plans, though, and so as soon as he heard the bell for the door ringing, he began packing it away.