The Forbidden Forest near Hogwarts School of Witchcraft and Wizardry is a strange and mysterious place that stretches for acres. There are glens where the canopy is so thick that the skies cannot be seen. There are glades where the sunlight shafts through the trees pleasantly. A large creek – or perhaps it's a small river – snakes its way through the forest, bringing life-giving water to both glen and glade. In places, the creek runs slow and wide, and ground nearby is marshy and treacherous. Other places it runs faster.
It is said that on certain nights of the year, the centaurs dance. No other race has ever seen this, for the horse-people are protective of their secrets. All the same, when the moon is high in the summer sky, the drumming of a thousand hooves echoes through the woods. It can be heard easily from Hogwarts, though few know what it means.
One knows it very well. Firenze hears the pounding echoes, even as the call of the moon sounds in his blood. He has denied it since his exile. Tonight, though, he does not resist. For the first time in years, he leaves his sanctuary behind and steps within the bounds of the forest.
His feet remember the way. He makes no effort at stealth; his people know the forest too well. As he approaches the glade, a shadow looms up in front of him, and he halts, tensing.
"Firenze." The voice is familiar, the echoing hoofbeats a counterpoint to the words.
"Sindar."
"Your sentence is not lifted."
"I know."
"You are to be killed on sight."
"Then come and kill me, or die trying." A formal challenge.
Sindar hesitates. Custom dictates that he must fight with the rebel, yet he is curious. "Why did you come back?"
"To dance." Firenze has not relaxed his stance, and now he moves forward, challenging the other stallion. "Will you fight or no?"
Sindar's legs and flanks are unscarred; he has not fought except in practice. He sees the marks of battle on the older centaur, marks caused by things other than slashing hooves. He retreats. "I… do not want to fight you."
"If you do not fight," Firenze presses his advantage, "you too will be exiled and condemned to never dance again." He has heard what Sindar has not – their voices have attracted the attention of the others. He repeats the challenge. "Come and kill me, or die trying."
Slowly, reluctantly, Sindar nods. "I accept."
It will be a fight to the death. That is the custom.
They crash together, locked in combat, the two centaurs. Sindar is marginally faster, but Firenze is heavier, with a longer reach. He has fought before. The racket draws the other centaurs away from their dancing. They watch quietly, making no effort to interfere.
Firenze uses his greater weight to advantage; he forces the younger stallion back, and nearly knocks him off his feet. It takes Sindar a moment to regain his balance, and in that moment Firenze wheels and lets fly with his hind feet, catching Sindar in the ribs. By the time Sindar recovers, Firenze is facing him again, untouched and not even breathing hard.
It is over soon enough. Youth is no match for experience, and Sindar stumbles and falls, bleeding from half a dozen deep slashes. Firenze looks down at him, then at the other centaurs.
It is the custom of the centaurs that a victory in formal challenge absolves the challenger of his crimes. Firenze strides to the center of the glade and dances.
Custom can be turned to advantage.