"Did you ever see anything so childish?" observed he, indicating the envelopes. "A big, registered, sealed Chinese puzzle like that is just crying out to be opened. We would have seen the inside of that one even if it had been addressed to the Lord Mayor, and not to--well, someone in whom we are deeply interested, though he does not know it." Cary, who had been fascinated by the succession of sealed envelopes, stretched out his hand towards one of them. "Don't touch," snapped out Dawson. "Your clumsy hands would break the seals, and then there would be the devil to pay. Of course all these envelopes were first opened in my office. It takes a dozen years to train men to open sealed envelopes so that neither flap nor seal is broken, and both can be again secured without showing a sign of disturbance. It is a trade secret." Dawson's expert fingers then opened the twelfth envelope, and he produced a letter. "Now, Mr. Cary, if we had not known you and also known that you were absolutely honest and loyal--though dangerously simple-minded and careless in the matter of windows--this letter would have been very awkward indeed for you. It runs: 'Hagan arrives 10.30 p.m. Wednesday to get Cary's Naval Notes. Meet him. Urgent.' Had we not known you, Mr. Richard Cary might have been asked to explain how Hagan knew all about his Naval Notes and was so very confident of being able to get them." Cary smiled. "I have often felt," said he, "especially in war-time, that it was most useful to be well known to the police. You may ask me anything you like, and I will do my best to answer. I confess that I am aghast at the searchlight of inquiry which has suddenly been turned upon my humble labours. My son at sea knows nothing of the Notes except what I have told him in my letters, my wife has not read a line of them, and my publisher is the last man to talk. I seem to have suddenly dropped into the middle of a detective story." The poor man scratched his head and smiled ruefully at the Scotland Yard officer. "Mr. Cary," said Dawson, "those windows of yours would account for anything. You have been watched for a long time, and I am perfectly sure that our friend Hagan and his associates here know precisely in what drawer of that desk you keep your Naval Papers. Your flat is easy to enter--I had a look round before coming in to-day--and on Wednesday night (that is to-morrow) there will be a scientific burglary here and your Notes will be stolen." "Oh no they won't," cried Cary. "I will take them down this afternoon to my office and lock them up in the big safe. It will put me to a lot of bother, for I shall also have to lock up there the chapters of my book." "You newspaper men ought all to be locked up yourselves. You are a cursed nuisance to honest, hard-worked Scotland Yard men like me. But you mistake the object of my visit. I want this flat to be entered to-morrow night, and I want your Naval Papers to be stolen."