Barlow smiled at this polite dismissal and, stating that he would be at headquarters for the rest of the evening and that they would know where to reach him after that, left the office—decidedly doubtful as to Thurber's ability to read the message.
Long after midnight Gene answered a ring from the phone beside his bed and through a haze of sleep heard the voice of the navy librarian inquiring if he still had the other papers which had been in Doctor Albert's bag.
"No," replied the operative, "but I can get them. They are on top of the chief's desk. Nothing in them, though. Went over them with a microscope."
"Just the same," directed Thurber, "I'd like to have them right away. I think I'm on the trail, but the message is impossible to decipher unless we get the code word. It may be in some of the other papers."
Barlow found the librarian red-eyed from his lack of sleep and the strain of the concentration over the code letter. But when they had gone over the papers found in the black bag, even Thurber had to admit that he was checkmated.
"Somewhere," he maintained, "is the one word which will solve the whole thing. I know the type of cipher. It's one that is very seldom used; in fact, the only reference to it that I know of is in Jules Verne's novel The Giant Raft. It's a question of taking a key word, using the letter figures which denote this, and adding these to the letter figures of the original letter. That will give you a series of numbers which it is impossible to decipher unless you know the key word. I feel certain that this is a variation of that system, for the fact that two letters appear together so frequently would seem to indicate that the numbers which they represent are higher than twenty-six, the number of the letters in the alphabet."
"One word!" muttered Barlow. Then, seizing what was apparently a memorandum sheet from the pile of Albert's papers, he exclaimed: "Here's a list that neither the chief nor I could make anything of. See? It has twelve numbers, which might be the months of the year, with a name or word behind each one!"
"Yes," replied Thurber, disconsolately, "I saw that the first thing. But this is October and the word corresponding to the number ten is 'Wilhelmstrasse'—and that doesn't help at all. I tried it."
"Then try 'Hohenzollern,' the September word!" snapped Barlow. "This message was presumably written in Berlin and therefore took some time to get over here."
"By George! that's so! A variation of the 'clock code' as well as Verne's idea. Here, read off the letters and I'll put them on the board with the figures representing Hohenzollern underneath. Take the first fifteen as before."