The Sacred Knife: Book 1 of the Pegasi Chronicles (2nd Edition)

A young boy is thrust into the timeless war between good and evil, between the forces of the Light and the forces of the Dark. He's the product of two worlds which gives him the power to destroy the immortals, evil beings who maintain their immortality by human sacrifice. He is not aware of his powers. However, the immortal beings are and their goal is to kill the boy before he becomes aware of who and what he really is.
Attempts to kill the boy fail but leave him orphaned and seriously injured. With his parents dead he's sent to live with his uncle, an emotionless man with a dark mysterious past. Neither is happy with the arrangement, and both remain unaware that evil forces are still trying to find and eliminate the boy. The large, isolated mansion provides the perfect location to enable them to assassinate the boy.
The boy's only ally and friend is another boy who calls the mansion his home. Only problem is - that boy has been dead for over 160 years.