The Forgotten — Stephen R. George

The Citadel was supposed to be the safest possible place to live. No crime. No worries. A haven for those fleeing the dangers of city life. But even the Citadel offered no protection against the blood-hungry horror that dwelled in its depths.

Only ten-year-old Mark Sullivan knew about the creature that stalked the building's secret shadows. It talked to him, called him "friend," begged him to unlock the grate that imprisioned it underground. And though Mark knew he should stay away, he was no match for the deadly call of THE FORGOTTEN.