What the Night Knows by Dean Koontz

What the Night Knows: A Novel - Twenty years ago, John Calvin’s family was killed.  John was 15 and killed the murderer.  Today, there are families being killed with the same MO.  John’s family is a target.  Each member of his family has experiences that they are not telling the other members, because to do so they believe would invite ridicule.  When John finally consults a priest, he is referred to a psychiatrist.  And the defrocked priest, who did do exorcisms, refuses to help.  John must protect his family without outside help.