The Time Of His Life
In this sequel to IN THE NICK OF TIME, Andy Mackpeace, on a class trip to the Historical Society, hears a dead boy calling to him from a photograph of a boys' camp from 1925: "Who killed me? I was murdered here."
Andy and Miranda, using the incense sticks, time travel to solve the mystery. Unprepared for the evil that stalks there, they race against time to find a killer and put a ghost to rest.