Harry's leg aches. It sends shivers of pain lancing up and down his back as he stalks up and down the hallways of Grimmauld, the walls closing in on him as he sinks deeper into the house. They settle in the base of his spine like fire, like pins and needles, like a numbness that still hurts. He leans more and more into his right leg with every step, dragging the left behind him like the useless thing it is.
He relives the moment over and over again. Remembers the bright flash of light as the hex came darting from the darkness towards him, the crackle of it dancing up his leg with lashing sparks of pain. The way his body had stopped responding to him and crumbled away like uncertain ground, sending him crashing to the floor in an ungraceful, but still deadly, heap. He doesn't remember casting the Jelly-Legs curse back at his attacker or the flight of stairs behind the wizard—though it's all he can think about now.
The awful sound of a body sliding down wooden treads—the hollow thump of it so much like his stumbling steps—and picking up speed, a man's voice raised in terror, only to break off into silence after one single crack, haunts Harry.
The Mediwizards couldn't explain the limp or the lingering pain. They healed it to the best of their ability, and their diagnostics and tests all said the same thing: he was fine. But as he lay in his hospital bed, lights out and eyes open, it ached and kept him awake, and in the hallway outside, he heard footsteps like someone falling.
Indefinite leave, they said. Take some time for yourself. Get your mind right. Nothing to worry about, of course. Back to work in no time.
Weeks since then, and nothing. No owls, no Floo calls. Just idle minutes for him to remember everything that came before and for his leg to whisper to him with a voice like agony.
The letter, its parchment a pale beige against the dark and dingy front mat, is an excuse. An escape. He picks it up, reads it, and then packs his things—not many, just enough, just what he needs. He leaves Grimmauld behind him like the mausoleum it's becoming, its only slowly-dying occupant escaping before he can't stand to breathe anymore.
Forgotten on a table, green ink winking in the half-light of an untended fireplace, the letter sits.
If you would like it, the position of Defense Against the Dark Arts professor has come available for the next school year. Please let me know if you'll consider taking it. I would dearly love to see you again.