Laurence Vanderlyn, unpaid attache at the American Embassy in Paris, strode down the long grey platform marked No. 5, of the Gare de Lyon. It was seven o'clock, the hour at which Paris is dining or is about to dine, and the huge station was almost deserted.

The train de luxe had gone more than an hour ago, the Riviera rapide would not start till ten, but one of those trains bound for the South, curiously named demi-rapides, was timed to leave in twenty minutes.

Foreigners, especially Englishmen and Americans, avoid these trains, and this was why Laurence Vanderlyn had chosen it as the starting point of what was to be a great adventure, an adventure which must for ever be concealed, obliterated as much as may be from his own memory--do not men babble in delirium?--once life had again become the rather grey thing he had found it to be...