They are the world's best-kept secret - an underground society whose eternal cause is to protect the world against the dark creatures and evil forces that inhabit the night. Now Sentinels are being targeted, murdered and turned as the fury of an ancient evil is unleashed once more. And when 15-year-old Nicholas Hallow's parents are killed in a suspicious train crash, the teenager is drawn into a desperate struggle against malevolent powers. Sentinel is the first book in the Sentinel Trilogy - a world of unconventional heroes, monsters, murder and magic.