Guy Fawkes Night, 1857. Joel Heygate is the popular stationmaster at Exeter St David's railway station - an impressive figure of a man replete with frock coat and top hat, bushy eyebrows and walrus moustache. But when the charred remains of a body are discovered in the embers of the town's annual Bonfire Night celebration, everyone is horrified when it becomes clear that they belong to Mr Heygate.

Mr Gervase Quinnell of the South Devon Railway contacts Scotland Yard for their assistance, and Superintendant Edward Tallis sends the Railway Detective Inspector Robert Colbeck and his assistant Victor Leeming to Exeter with all due haste. They quickly unearth three suspects, but are they missing something?

It is only when Heygate's diary turns up unexpectedly that the truth becomes clear and a fourth suspect emerges. As Colbeck closes in on the killer, he finds himself in mortal danger - can justice prevail?