It was the early six century B.C.E in Ireland. The Druid Order were at the peak of power for the Celtic tribes. They were not truly human for they were spiritual in nature crossing into the next world to commune to the gods on behalf of mankind. They could foresee the future, do spells, and many other unknown didn't age like humans, they were of immortal blood.
The head Druid of the time known as Adrian was an old wise man who had kept the order in peace for wars had raged across the Emerald Isle. The Unseelie Court and the Seelie Courts were the main races at war with each other over territories. This also led the involvement of the Druids who were the island's guardians.
But fate changed forever when the Eagle appeared in a vision and the arrival of the Roman General Julius Caesar. He tried to wipe out the Druid Order for good in a massacre known as "The Massacre of the Mystics." But those who had survived tried to make a pact with one of the most untrustworthy, wildest races known to them, the Fey.
Both rulers of the Unseelie Court and Seelie Court refused to help out the guardians. So they went to the sacred worshiping site and made a pact with the island's more natural beings known as the elemental.
There was just one catch in exchange for elemental powers they must die early to help renew the veil of the island. So the bond to the spiritual world will be severed and they would age like a human. Unless they come across the prophetic child who has the power to stop the collapse of the veil completely and to bring peace to the warring races.
The Druid Order destroyed Julius Caesar by cursing him into his own death years later.
As the centuries went by, the descendants of the Druid Order is fading away and one is now left to seek out the prophetic child. His name is Caden.