Reluctant sleuths Mal and Vinn are again coerced into investigating a death, this time of an Amish teenager found murdered at a zoo in Chicago. Navigating the unfamiliar world of the Amish proves difficult for the two outsiders. On the verge of giving up, the murder of a young suburban man with no apparent link to the teenager is connected by a singularly bizarre and grisly detail and spurns them on.

Trying to tie a girl's life of horse-drawn buggies and no electricity to that of a man barely out of high school living in his parents' basement brings together the old gang and a collection of college students as they traverse a dark path that draws them into the realm of a cultist whose belief that celestial beings will visit Earth offers both a possible solution and the risk of death to everyone involved.