Dumbledore was in his office, looking over some letters he had received from his contacts - rumours of attacks on Muggles and muggleborn families, isolated, and yet something lurking behind it, suggesting just the lightest hint of organisation, when he heard the horn blow.
A centaur's warhorn. It had been a number of years since he had heard the call and he had spoken with the herd's elders in recent weeks, so this was something else. He had assured them students were staying out of the Forbidden Forest except for the agreed times, such as the groundskeeper and keeper of the keys going forth as needed. But the groundskeeper was off on an errand, so Dumbledore considered the fact he would need to visit in person - for the centaur's warhorn to sound, something important must be afoot, and in the interests of co-operation with magical creatures, he made a noise and Fawkes looked up.
A gesture of his wand and the window opened, and Fawkes made a beeline for it - with Dumbledore catching Fawkes' tail in a practised manner, and they flashed out in a burst of flame, reappearing somewhere near the edge of the Forest.
Fawkes flew low, and Dumbledore landed gently a short distance away from the centaur, arms raised, wand not drawn.
"I don't believe we have met, I'm afraid. I am Albus Dumbledore, headmaster of the school - the castle. How can we be of assistance?" He was expecting to get the lecture about the humans and their interference not being wanted, but clearly the centaur was concerned.
The centaur, however, merely nodded his head and pointed off to the west. Dumbledore followed the outstretched arm and saw the wounded unicorn.
"Oh." He said, rather perfunctorily. "That rather complicates matters. Of course, you must understand that I cannot readily permit you free reign of the school grounds - as your elders agreed, but I will get our foremost local expert on unicorns to attend to its needs and we will accompany it back to its herd. I believe some of your village are familiar with Professor King, our Care of Magical Creatures lecturer?"
He fished a small piece of parchment out of a pocket, made some marks on it with his wand in lieu of a quill, and gave it to Fawkes who had settled nearby. "I'm sorry to treat you as a messenger, my friend, but it is urgent that we get word to the Professor." Fawkes made a noise, a touch petulant but mostly understanding, and was gone back to the castle.
Turning back to the centaur, Dumbledore said, "Are you the centaur that was injured some weeks back? I believe the others referred to you as Lincei - may I call you that?" The centaur, if he had heard, stood by, stony-faced. "Ah, well, the good professor will no doubt be here shortly, and we can all go on our way."