That night at eleven o'clock Mr Merton Mansfield returned, was cheered loudly by a huge crowd gathered outside the hotel, and waited below chatting for nearly half-an-hour before he retired to his room. The room was numbered 146--the best room of a suite on the first floor-- and to this room the young German, the catspaw of Ortmann, had gone about a quarter past eleven, gaining admission through the private sitting-room next door. On entering he, quick as lightning, took down one of the vases from the mantelshelf and replaced it by another exactly similar which he drew from beneath the light coat thrown over his arm. Then, carrying the vase with him concealed by his coat, he slipped quickly out again unobserved, not, however, before he had poured into the other vase some bird-sand so as to make them both of equal weight when the maid came to dust them on the morrow. The conspirators left nothing to chance. In that innocent-looking vase he had brought was one of the most diabolical contrivances ever invented by man's brain. To the explosive needle the tiny clock had been attached and set to strike at half-past two, an hour when the whole hotel would be wrapped in slumber. The effect of striking would be to explode the needle and thus break a thin glass tube of a certain liquid and set over a piece of sponge saturated by a second liquid. The mixing of the two liquids would produce that terribly deadly poison-gas which, escaping through the perforation, must cause almost instant death to any person sleeping in the room. Truly, it was a most diabolical death-trap. Ten minutes later Mr Merton Mansfield, quite unsuspicious, entered the room and retired to bed, an example followed by the assassin Schrieber, who had a room on the same corridor a little distance away. At nine o'clock next morning Seymour Kennedy, bright and spruce in his uniform, descended to the hall and inquired of the head-porter if Mr Merton Mansfield had left. "Mr Mansfield is an early bird, sir. He went away to London by the 6:47 train." The air-pilot turned upon his heel with a sigh of relief. Two hours later, however, while seated in the lounge with Ella, prior to returning to London, Kennedy noticed that there was much whispering among the staff. Of the porter he inquired the reason. "Well, sir," the man replied, "it seems that a maid on the first floor, on going into one of the rooms this morning, found a visitor dead in bed--Mr Sommer, a Swiss gentleman who arrived last night. The place smells strongly of cloves, and the poor girl has also been taken very ill, for the fumes in the place nearly asphyxiated her." Seymour again returned to Ella and told her what had occurred. "But how did you manage it?" she asked in a low whisper.