Schewesen was known to have been making researches into the possibility of stabilising Nitrogen Trichloride (NCl3), the most powerful explosive known to science, but, as far as contemporary methods of preparation have progressed, entirely without practical use, since even particles of dust settling upon it from the atmosphere are sufficient to detonate it. Schewesen had announced a few days before his death that his experiments promised an epoch-making success. He has left no notes behind, however, and it is to be feared that his knowledge has died with him. Teal read the paragraph a second time, for this premature obituary notice did not appeal to his sense of humour. He was quite certain that Carl Schewesen was alive and in London, and, Storm returning with Mattock at that moment, he pointed to the column and vented his surmise. Storm read it through, and looked grave. "NCl3," he murmured. "That sounds like more fun!" "Is it very powerful?" asked Teal, and Storm smiled. "If a small saltspoonful went off between us now, they'd be able to bury us in matchboxes!" he said. It was then that Teal noticed the presence of Mattock, and turned to scowl at the man. Mattock had been looking over the detective's shoulder unobserved, and his smile showed that he had heard the conversation. "I know all about Carl," Mattock said. "But the problem ought to amuse the flatties for some time. Flatties, I think, was the term Nosey used?" Teal was struck by the change in the man's manner since he had met him in Walton Street Police Station. Then, Mattock had had the truculence which comes of an inferiority complex; but that had now dispersed as though it had never existed. In spite of the shabbiness of his clothes and the ugly lines which prison had cut in his face, he bore himself with a calm confidence that annoyed Teal. It annoyed him because he could not understand it. It was so out of keeping with the part of the lag under supervision. Truculence was regular, and cringing was also in order, though less common. So, too, was friendliness. But superiority--no. "You look pleased with yourself," said Teal glutinously, falling back into his _rôle_ of _ennui_ personified. "So I feel," agreed Mattock. "Captain Arden has very kindly permitted me to be released." He glanced at his wrist. "It's just lunch time. Thank the Lord I'm spared the culinary abortions you serve to persons in custody." Teal's jaw dropped. "Is that true?" he asked, and Storm nodded. "I'm sorry, Inspector," he said officially. "I don't think any of the charges against this man will stand. You will, however, keep him under observation." "I will!" asserted Teal grimly. Mattock raised his hat and sauntered to the door with a smile. There, he paused. "I should keep an eye on Uncle Joe, too," was his parting shot. Teal stared sombrely at the door through which the man had passed. He shook his head sorrowfully.