It begins with a passenger ferry in the English channel, sailing from Newhaven to Dieppe. Captain Hewitt sees a yacht adrift, with a man lying motionless on the deck. He sends a small boarding party and they find that the man has been shot dead, as has another man they find in the cabin.
There is no sign of a murder weapon, or the murderer.
Another man arrives on a motor launch. He is John Patrick Nolan, and he had come to join two of his partners in Moxon's General Securities on a business trip, to meet a French financier named Pasteur in Fécamp. He identifies the two dead men as Paul Moxon, chairman of the firm, and his vice-chairman, Sydney Deeping.
Back in England the investigation falls to the Sussex Police, and to Inspector Joseph French of Scotland Yard