My first precaution was to soften the sealing wax with a match, so that I could unwrap the bottle without tearing the paper, and, if necessary, so replace it that no suspicion that it had been tampered with should be aroused. The bottle might prove useless as a clue. In that case we should have to seek further, and to replace the bottle in Humber’s trunk in such a condition that he must inevitably see that it had been opened would certainly arouse his suspicions and defeat our object.
I soon had the paper opened out. The bottle of medicine seemed genuine enough. It bore the label of a well-known West End firm and the name of Mr Humber. I tasted the contents.
“Cough mixture” was my comment, and Captain Jackson at once confirmed me. “Humber never had a cough,” he remarked reflectively.
“Now for the paper,” I said, and began examining it. It was perfectly blank, and I was experiencing a pang of disappointment when, catching on the paper the reflection of the swinging lamp, I detected in one corner a faint, glistening line. Lemon juice, I was confident.
Under appropriate “treatment” a number of neat figures arranged in groups of three sprang into vivid prominence on the inside of the paper wrapping. They ran:
123—5—8; 27—32—6; 46—23—11;
294—12—3; 18—1—8;
and so on.
I swiftly copied out the figures for safety, and handed the original paper to Captain Jackson, who, on board his own ship, was, of course, the supreme and unquestioned authority, and I wanted his full approval and support to any action that might be necessary. The figures were meaningless as they stood, but I had not forgotten old Heinrich’s systematic search for that odd volume of Royal Love Letters. I had my copy in my bag and fetched it at once.
With such an obscure book as the key to the cipher there was no need for any further elaborate precautions, and we hit upon the solution of the difficulty at once. On page 123 the eighth letter on the fifth line was “B;” on page 27 the sixth letter in the thirty-second line was “r”; and in a few minutes I had decoded the word “Brixton.” Going on, I found that the message conveyed the news that Number 24, — Road, Brixton, had been wrecked by one of the bombs dropped in the recent raid; that a man, a woman, and two children had been killed. The spots where the other bombs had fallen were accurately described, and it was stated that they had done no damage beyond blowing holes in the roads and bursting gas and water mains. Every word was accurate.
And the key to the whole problem was the mysterious advertisement for a lost trinket in the Petit Parisien. That simple advertisement, so apparently innocent, had announced to Blind Heinrich the enemy’s change of code! And without the book to which it referred no intelligence on earth could have deciphered the disorderly mass of figures which lay before our eyes!
“Well, I think we have got them now, Captain,” I said, “and I am sure the Government will be deeply obliged to you for your assistance. But how am I going to get this fellow? If he lands in Norway he will be out of our power.”