A few days previously a mysterious explosion had occurred in some public gardens at Mile End. While a keeper was clearing away a pile of rubbish he found a curious-looking metal cylinder lying in a flower-bed, and while he was examining it it exploded with a tremendous report, injuring the man so severely that he had to be taken, in a very critical condition, to the East End Hospital. A search by the police had a curious result. In other flower-beds a number of similar cylinders were found. They were very tiny, being only about an inch and a half in length and about a quarter of an inch in diameter. They contained a substance which was evidently the explosive. At one end a piece of wire was attached, evidently as a means of exploding them, and at the other end was a strip of soft lead. Morgan showed me some of the cylinders, and frankly confessed his ignorance of what they contained. "I thought I knew every explosive in existence," he told me, "but this is something entirely new. It must be tremendously powerful, judging by the size of the cylinders and the effect of the explosion on the unfortunate gardener who found the first one." As I held one of the small cylinders, studying it with great care, an idea came to me. "May I borrow this for a few days?" I asked. "I think I may be able to help you." "Certainly," replied Morgan; "but be careful. We don't even know how it is exploded." Next day I was in Paris, and took train to Vemeuil l'Etang, some thirty miles from the capital, where I called on the manager of a certain well-known factory. When I showed him the little cylinder he examined it with minute attention and carefully withdrew some of the mysterious explosive. This he placed under a microscope and a moment later said: "Monsieur is undoubtedly correct! It is some of our product, herbethite, the invention of our chief director, Mr Herbeth, and the most powerful explosive known to modern science. None has been used in actual work yet, and the only sample that has left our factory is that which was stolen. It is a great secret." "Has some been stolen, then?" I asked quickly. "Yes. Fortunately we discovered the thief--a workman named Pasquet--and we thought we had recovered all that had been taken. Evidently we were wrong and some of the stuff has got into bad hands. Pasquet is awaiting trial by the Assize Court of the Seine." I returned to Paris and saw the Minister of Justice, to whom I made a certain proposal. Not without demur, he finally agreed, and I went to the prison armed with authority for a private interview with Pasquet. I met the thief in a small room in the governor's quarters of the prison. I found him to be a man of about thirty, quite obviously of the hooligan type, and I soon guessed from his conversation that he had been in the first place the tool of others, who, when they had made use of him, had abandoned him to his fate.