A Traitor in London by Fergus Hume — Read

Strong man as he was, Van Zwieten reeled half-fainting against the wall. It was true -- the box was gone! In a flash he realized his peril. For that box held little that was not of a highly compromising nature. Once its contents were seen by the authorities -- as it would seem they must be -- he would be arrested as a spy, imprisoned, perhaps hanged. No ingenuity or lying on his part could explain away the damning evidence of the papers. They spoke for themselves.

What a fool he had been not to have forwarded them to Leyds in the morning as he had intended to do. Now it was too late, and nothing remained but to fly to Pretoria and to throw in his lot openly with his employers. Useless now to think of going out as correspondent to an English newspaper, even were he able to manage his escape from London. Those in command at the front would surely be advised of his true character by the home authorities; and not only that, but he would be unmasked in a country under military law, where a spy such as he would receive but short shrift. Fly he must, and that at once. He must get to the Continent, and take ship for Delagoa Bay. The game was up in England; there remained now only the Transvaal.