With an exclamation of annoyance Mr. Martin turned once more to the letter. “Dear Sir, I venture to address you upon a subject which will no doubt interest you,” it ran. “I have recently acquired a lease of the premises No. 407, Praed Street, which I understand, were in your occupation up till some fifteen years ago. Since you vacated them, these premises have been occupied by a clothier, who did not require the extensive cellarage, which was boarded up. In the course of certain alterations which I am having made to the premises, the entrance to the cellars has once again been opened. In the course of my investigations I have made a most interesting discovery in the small cellar beneath the back office. “I should perhaps report this discovery to the authorities, but I have thought it best to consult you upon the matter before doing so. This letter should reach you by the first post to-morrow (Saturday) morning. I should be glad if you could make it convenient to meet me on the premises at 2 p.m. that day, when the workmen who are at present employed there will have gone. I can then show you my discovery, and we can consult upon the most suitable steps to be taken in the matter. Should you not find this convenient, I shall assume that the subject does not interest you, and shall report the matter forthwith to the police. Yours faithfully, John Lacey.” A blackmailing letter, without a doubt, Mr. Martin could see at a glance. But what on earth could the fellow have discovered? Fifteen years ago, when Mr. Martin moved from Praed Street to the Barbican, he had taken the utmost care to destroy every trace of the purpose to which that little cellar had been put. He racked his brains to try and think of anything that could possibly have been overlooked, but without success. Even those ingeniously contrived recesses in the walls had been torn out, leaving nothing but the bare brick. Mr. Martin had done the work with his own hands, not caring to trust anyone else with so delicate a matter. Yet, after all, in spite of all his care, he must have left some clue, which this infernal fellow Lacey had somehow blundered upon. He brushed aside as absurd the suggestion that “Lacey” could conceal the identity of one of those with whom he had done business, who knew the secret of the cellar and had adopted this clumsy plan to blackmail him. The circle of his secret clients was a very narrow one; he knew them all and was well aware that blackmail was neither in their line nor in their interest. The expert in acquiring jewellery concentrated upon his particular art; he did not descend to blackmail, especially of the one man through whose agency he was able to dispose of his spoil. No, there was no doubt about it, a slip had been made, a slip which had lain undiscovered all these years, through the circumstance that his successor, the clothier, had found no use for the cellars and had boarded up the entrance to them.