Long lost - David Morrell

Brad Denning's brother Petey is long lost.

Frozen in time as a skinny nine-year-old bicycling away from his uncaring older brother, Petey haunts Brad's consciousness.
To this day, within his prosperous life, Brad knows with certainty that he was responsible for the boy's disappearance.
He knows how much his mother and father suffered and that nothing can ever bring Petey back - until a stranger walks into Brad's life.

Suddently Brad is confronted by a man who claims to be his brother and whose tale is one of wandering, pain, and survival.
As Brad gradually puts aside his suspicions, Petey makes himself at home in Brad's life.
Then everything is shattered.
Petey again disappears.
Only this time, he's taken Brad's wife and child with him.