"We are going to call on Dr. Tresman, in Montagu Street," he said, stopping a taxi. "You will tell him that you have reason to believe that his house is being watched, and will be burgled on the first opportunity. If the opportunity is given, it may happen to-night, which will suit us admirably, because we have got to keep watch every night in his room until it is burgled. Of course, you will tell him who you are, and get his permission. We don't want to have to commit burglary ourselves in order to catch the thief." "Why do you expect this particular doctor will be visited?" I asked. "It is part of my theory," was all the explanation I could get out of him. Dr. Tresman was a man in the prime of life, and evidently believed himself capable of dealing with any thieves who visited him. I told him that the man we expected was no ordinary thief. "A gang at work, eh? I have been out of town for a little while holiday-making, and part of my holiday consists in not reading the papers. Of course you may keep watch, and I shall be within call should you want help." "You had better leave it to us, doctor," said Quarles, who, for the purpose of this interview, posed as my assistant. "Come, now, if it means a rough-and-tumble, I should back myself against you," laughed Tresman, drawing himself up to his full inches. "No lack of muscle, I can see, doctor, but then there is my experience." "For all that, you may be glad of my muscle when it comes to the point," was the answer. At nine o'clock that night Quarles and I were concealed in the doctor's room, Quarles behind a chesterfield sofa in a corner, while I crouched close to the wall behind one of the window curtains. We had decided that the most likely means of entry was by a window at the end of the hall, and we expected our prey to enter the room by the door. We had got the doctor to put a spirit tantalus on the sideboard, also some biscuits and a box of cigarettes. We were anxious to reproduce the circumstances of the burglary at Sir Joseph Maynard's as nearly as possible, for Quarles declared it was impossible to say what significance there might be in the man's every action. So we waited--waited all night, in fact. Nothing happened. "Something alarmed him," was all Quarles said when we left the house in the morning. He showed no disappointment, nor any sign that his theory had received a shock. The next night we were on the watch again, concealed as before. By arrangement, the house retired to rest early. So slowly did time go that half the night seemed to have passed when I heard a neighboring church clock strike one, and almost directly afterward the door of the room was opened stealthily and was shut again.