April 1867. Amid the usual bustle at King's Cross, a large wooden box is loaded onto a train bound for Lincoln, its watchful escort insistent it remain in sight. But a daring robbery derails those plans, leaving behind a dead man and a vanished treasure.

Detective Inspector Colbeck is called in after a plea from the Dean of Lincoln Cathedral to find the killers and recover a priceless silver model of the cathedral. With the annual Horse Fair flooding the city with visitors, Colbeck and Sergeant Leeming must navigate a web of confusion to track the culprit, although Colbeck grows certain the thief is still close at hand. But time is short, and the Railway Detective faces one of his most complex cases yet.