Disclaimer: I don't own Harry Potter and Percy Jackson.
Prologue:
The sky was full of clouds. A dark shadow covered the whole scenery. A light breeze was blowing, making everyone's hair stand on end. At the edge of the Forbidden Forest, there were flickers of lamp brightening up a narrow and bendy path which was hidden behind a clump of trees. There stood two figures. One of them was a creature that was part horse part man. The top half of his body was a man with white-blonde hair, but the other half was a slender, golden figure of a horse. He had eyes which were astonishingly blue, like sapphire. The other one was a tall and very old man with long silver hair. He was wearing a long purple robe and half-moon shaped glasses. He had twinkling blue eyes and a long aquiline nose.
"I need your help.", the old man spoke in a quiet voice.
The centaur listened, but didn't answer. He looked at the stars in the sky for a moment and then sighed deeply. He turned to the old man and said with respect: "What can I do for you?"
The old man slightly smiled: "As you know, Lord Voldemort has returned and been calling for his followers. The situation is very dangerous for all of us. The problem is that the Ministry don't want to believe in his return, which will hinder us from preparing defences against him. So I hope if you foresee anything about this, please tell me."
"Thanks for believing in me, but you know that I can't tell you anything.", the centaur paused, then continued, "However, I know who has the ability to help you. He is my cousin."
"Your cousin?", said the old man with surprise but also hesitation.
"Yes, and don't worry. He isn't like my kind here. He is really wise and I think he will be willing to help you. I will contact him if you like."
"That will be great. Thank you, Firenze."
"Glad if that could help. See you later, Professor Dumbledore."
Like that, the conversation was over. There was only light from the moon piercing through the dense foliage. The forest became dark and quiet again.