“That sounds plausible,� Fay said. “Then it is no hoax?�
“It’s straight goods, Fay! The five thousand sheets in these three boxes contain the chemical formulae for the thirty-six dyes. The devil of it is, we lost the key, in—the country north and east of here. You’re going to get that key for us!â€�
“Just a moment. Isn’t it possible that the whole thing is a blind?�
“Be clear!�
“I mean that the lines of letters, thirty-two or three on each page, are there for a gull?�
“Go on!�
“They might be a gull for fools to go mad about. The real cipher may be within the lines. That also is a common practice at Dartmoor. Men have received letters from the outside which are written with lemon juice between the lines. All they did was to heat the paper and the message came out in brown ink.�
Sir Richard smiled broadly. “That has been thought of,� he said, glancing at MacKeenon. “To be frank, as I said, everything has been tried. We’ve even split some of the paper. We’ve tried every reaction known to science. We’ve bathed the sheets in oxalic acid and iodine. There was only one clue in this direction.�
Fay lifted his hand and fingered the pearl-pin in his cravat.
“That one clue,� continued Sir Richard, “was the