Smart as the Devil is a novel written by Felice Picano. It was first published in 1975.
Description[]
A novel about a twelve-year-old boy's devilish alter ego, in mortal confrontation with a very modern psychologist. The doctor needed a diagnosis - dual-personality? Possession? His search for the truth unfolds a death and several little horrors, immersing himself, the boy and the inhabitants of a sedate Connecticut household to the limits of rationality.