“The end of this cylinder--you can still feel the slime of the soap upon it--was first dipped into the soap solution, then thrust through the grating. The tap was turned down and a bubble formed, which was shaken off. From the ventilator,” he ran outside and jumped on to the table, “yes, I thought so,” he said, “he could see Marl’s head. Two or three of the bubbles must have been failures. One struck the pillow, but I should imagine that that was blown after his death; one struck the wall, you will find the wet patch, but one, and probably more, burst on his face. He must have been killed almost instantaneously.” Parr could only gape. “I thought it all out on the way here. The circular patch on the pillow reminded me of my own boyish exploits and their disastrous effect when I started blowing bubbles in the bedroom. And then when you mentioned the ventilator and the hissing noise, I was perfectly certain that my theory was right.” “But we smelt no gas when we came into the room,” said Parr. “The wind may have blown away the fumes,” said Derrick Yale. “But apart from that, the weight of the gas would send it to the floor, and by its own density it would spread evenly--look!” He struck a match, shielded it for a moment until it caught light, and then slowly brought it down to the floor level. An inch from the carpet the match was suddenly extinguished. “I see,” said Inspector Parr. “Now what about searching the place? Perhaps I can be of use,” suggested Yale, but his offer of help did not meet with any very gracious response. A small police audience, which had listened awe-stricken whilst Yale had developed his theory, could understand the inspector’s feelings. Apparently Yale did, too, for with a good-humoured laugh he made his excuses and went home. There are moments when the head-quarters police should be left alone with their own emotions. Nobody realised this more than Derrick Yale. Chapter XVIII. “Flush” Barnet’s Story Inspector Parr, after a further search, proceeded to the nearest police station to interview Mr. “Flush” Barnet. “Flush,” a depressed and weary man, had no illuminating information to give. The proceeds of his robbery lay upon the station-sergeant’s table, a miscellaneous collection of rings and watches, a perfectly valueless bank-book--valueless to “Flush,” at any rate--and a silver flask. But the most surprising circumstance was that in “Flush” Barnet’s pocket were two brand new bank-notes for a hundred pounds, which he insisted stoutly were his own property. Now burglars, and particularly the type of burglar that “Flush” Barnet was, are notoriously improvident people. They do not work whilst they have money, and with two hundred pounds in his possession, it is certain that “Flush” Barnet would not have attempted to break into Marisburg Place. “They’re my own, I tell you, Mr. Parr,” he protested, “would I tell you a lie?”