Hackness made no reply. On the whole he was wishing himself well out of it. That pillar of smoke would rise for many more hours yet. At the same time here was his great opportunity. There were certain experiments that he desired to make and for which all things were ready. They reached the scene of the catastrophe. Within a radius of five hundred yards the heat was intense. Nobody seemed to know the cause of the disaster beyond the general opinion that the oil gases had ignited. And nothing could be done. No engine could approach near enough to do any good. Those mighty tanks and barrels filled with petroleum would have to burn themselves out. The sheets of flame roared and sobbed. Above the flames rose the column of thick black smoke, with just the suspicion of a slight stagger to the westward. The inky vapour spread overhead like a pall. If Hackness's fog came now it meant a terrible disaster for London. Further out in the country, where the sun was actually shining, people watched that great cloud with fearsome admiration. From a few miles beyond the radius it looked as if all the ranges of the world had been piled atop of London. The fog was gradually spreading along the South of the Thames, and away as far as Barnet to the North. There was something in the stillness and the gloom that London did not associate with ordinary fogs. Hackness turned away at length, conscious of his sketchy breakfast and the fact that he had been watching this thrilling spectacle for two hours. "Have you thought of a way out?" Eldred asked. "What are you going to do?" "Lunch," Hackness said curtly. "After that I propose to see to my arrangements in Regent's Park. I've got Grimfern's aeroplane there, and a pretty theory about high explosives. The difficulty is to get the authorities to consent to the experiments. The police have absolutely forbidden experiments with high explosives, fired in the air above London. But perhaps I shall frighten them into it this time. Nothing would please me better than to see a breeze spring up, and yet on the other hand----" "Then you are free to-night?" Eldred asked. "No, I'm not. Oh, there will be plenty of time. I'm going with Sir Edgar Grimfern, and his daughter to see Irving, that is if it is possible for anyone to _see_ Irving to-night. I've got the chance of a lifetime at hand, but I wish that it was well over, Eldred my boy. If you come round about midnight----" "I'll be sure to," Eldred said eagerly. "I'm going to be in this thing. And I want to know all about that explosive idea." II. Martin Hackness dressed with less than his usual care that evening. He even forgot that Miss Cynthia Grimfern had a strong prejudice in favour of black evening ties, and, usually, he paid a great deal of deference to her opinions. But he was thinking of other matters now.