If you could leave your dreary life behind, knowing there could be no turning back, would you do it? This is the choice ultimately awaiting 15-year-old Mark Underhill in Peter Straub’s new chiller-thriller, “Lost Boy Lost Girl.”

Mark disappears shortly after his mother’s death. Is he the victim of a serial killer, a suicide — possibly in imitation of his mother — or is there something more sinister afoot?

These are among the questions that haunt Manhattan novelist Tim Underhill, who returns to his hometown of Millhaven, Ill., to attend Nancy Underhill’s funeral — and later, to search for his missing nephew.

Tim’s brother, Philip, had made a showy pretense of affection for Mark at his wife’s funeral. But Nancy’s suicide had driven father and son farther apart.

Mark, stalked by visions of a mysterious dark man, becomes obsessed with an abandoned house across the alley from his home. When Mark and his best friend, Jimbo, decide to break into the house, what they discover there will leave readers gasping.

Meanwhile, Tim learns that serial killer Joseph Kalendar had lived in the house on Michigan Street. Is the mysterious “dark man” the ghost of Kalendar? Could a young girl believed to be Kalendar’s daughter hold the key to Nancy’s suicide — and Mark’s disappearance?

Straub expertly twists the story from one viewpoint to another, across time and space, in different directions, back and forth between reality and the supernatural.

“Lost Boy Lost Girl” will linger in readers’ minds long after the final pages of this taut thriller.