When Jack Sainsbury descended the steps into Fitzjohn's Avenue and strode down the hill to Swiss Cottage station, he was full of grave and bitter thoughts. As an Englishman and a patriot, what was his line of action? That was the sole thought which filled his mind. He loved Elise with every fibre of his being, yet, on that evening, greater and even more serious thoughts occupied his mind--the safety of the British Empire. To whom should he go? In whom dare he confide? As he crossed from the Avenue to the station, another thought arose within him. Would anybody in whom he confided really believe what he could tell them? Lewin Rodwell and Sir Boyle Huntley were national heroes--men against whom no breath of suspicion as traitors had ever arisen. It was the habit of the day to laugh at any suspicion of Britain's betrayal--an attitude which the Government had carefully cultivated ever since the outbreak of war. On that day the Chief of the Military Operations Department of the War Office--in other words our Secret Service--had been--for reasons which will one day be revealed--promoted and sent to the front, leaving the Department in the hands of others fresh to the work. Such, alas! was the British Intelligence Department--an organisation laughed at by the Secret Services of each of our Allies. The folly of it all was really pathetic. Jack Sainsbury knew much of this. He had, indeed, been, through Dr Jerome Jerrold, a friend of his, behind the scenes. Like all the world, he had read the optimistic, hide-the-truth newspapers. Often he had smiled in disbelief. Yet, on that afternoon, his worst fears had in a single instant been confirmed. He knew the volcano upon the edge of which Great Britain was seated. What should he do? How should he act? In the narrow booking-office of Swiss Cottage station he stood for a moment, hesitating to take his ticket. Of a sudden an idea crossed his mind. He knew a certain man--his intimate friend. Could he help him? Dare he reveal his suspicions without being laughed at for his pains? Yes. He would risk being derided, because the safety of the Empire was now at stake. After all, he--Jack Sainsbury--was a well-bred Briton, without a strain of the hated Teutonic blood in his veins. He would speak the truth, and expose that man who was so cleverly luring the Empire to its doom. He passed before the little pigeonhole of the booking-office and took his ticket--an action which was destined to have a greater bearing upon our national defence than any person even with knowledge of the facts could ever dream. CHAPTER THREE. THE HOUSE IN WIMPOLE STREET. Just before eleven o'clock that night Jack Sainsbury stopped at a large, rather severe house half-way up Wimpole Street--a house the door of which could be seen in the daytime to be painted a royal blue, thus distinguishing it from its rather dingy green-painted neighbours.