October 31st 1949. Smog chokes London as the body of Jack Pym floats in the oily waters of the Regent's Canal near Marylebone station. Presumed a suicide, it looks a simple case, but D.I. Vignoles of the British Railways detective department suspects foul play. Pym's wife is telling lies, and nothing is quite what it seems. As the Pyms' private lives are uncovered, darker and more deadly truths are revealed - and there are those prepared to kill to keep these secrets safe. The story races between Marylebone and Leicester behind grimy steam engines on the Great Central line, reaching a dramatic conclusion in Southampton docks...