Don't Come Out is the story of Brian and Bridget Sykes, a young Dublin couple, and their eight-year-old son Danny. One day, evil in the human form of Geoffrey Staines is waiting when Bridget and Danny return home from shopping. Bridget is attacked and injured, but worse, Danny is gone. Detective Michael McCann begins investigating what he realises early on will be a sinister case. Between himself and Brian, they realise, too late, who has taken Danny.

Staines in captured and sent to trial for what is assumed will be an open-and-shut case, but twisted circumstances and an over-vigilant judge intervene to send the killer to prison for a much shorter time than Brian and Bridget, by now estranged, could ever have imagined. Brian makes a statement in court, at the end of which he turns to Staines and says simply "Don't come out."

Seven years later, Staines is released. Brian is waiting. Detective McCann is drawn, albeit reluctantly, back into the case. What follows is a journey into the darkest side of the human spirit. Brian has become more deadly and dangerous than anyone could have imagined, and he embarks on an unbelievable trail of revenge, retribution, and as he sees it, justice. Eventually McCann enlists Bridget's help to try and save Brian from himself. To bring him back from the dark world that has become his preferred place of residence.