The Charing Cross Mystery (Unabridged‪)‬

This story, originally published as Black Money in 1922, by Joseph Smith Fletcher (1863-1935), is a fast-paced thriller full of surprising twists and turns.  

Hetherwick, a young lawyer, becomes a witness to murder riding the train late one night. Of the two men who entered his train compartment, one drops dead, for no apparent reason, as the train pulls into Charing Cross station.