There was a German official of high importance living in the Calle Alfredo Menandez, although not at number 6 in that street.  The street was a short one with very few numbers in it; and it had occurred to the German official to point out to the postman in that street that if letters came to English names in that street of which the owners could not be discovered, they were probably for the governess of his children, who had a number of English relations moving about Spain, and was accustomed to receive their letters for them, and in any case, five pesetas would be paid for each of them.  Shortly after, letters had begun to arrive addressed to English nonexistent people in the quiet little Calle Alfredo Menandez, sometimes from Allied countries, sometimes from Holland, or from Port-Bou over against Cerbere in Spain; and every one of these found its natural way to the house of the German official.  The choice of English names had a certain small ingenuity in that, when passing through the censorship of Allied countries, they were a little more likely to be taken at their face value than letters addressed to foreigners.

So far so good.  But the German high official was a very busy person; and letters might find their way into his hands which were really intended for English persons and not for him at all.  Accordingly, to make all clear, to warn him that here indeed was a letter deserving his kind attention, that little trifling alteration in the date was adopted; as though a man writing on the 28th had mislaid the calendar or newspaper and assigned the 27th to the day of writing, and afterwards had discovered his mistake.  It was no wonder accordingly that hope ran high in both Fairbairn and Hillyard as they read through this letter; although, upon the face of it, it was nothing but a sentimental effusion from a sister to a brother.

“We have got to clear all this nonsense away first,” said Hillyard.

Fairbairn took the letter, and placing it on one of the developing dishes, poured over it a liquid from a bottle.

“That won’t take very long,” he said.

Meanwhile Hillyard busied himself with the second of the two white porcelain dishes.  He brought out a cruet stand from a cupboard at the side of the stove and filled the dish half full of vinegar.  He added water until the liquid rose within half an inch of the rim, and rocked the dish that the dilution might be complete.  Next he took a new copying-pencil from the pen-tray on his bureau and stripping the wood away with his knife, dropped the blue lead into the vinegar and water.  This lead he carefully dissolved with the help of a glass pestle.

“There!  It’s ready,” he said.

“I, too,” added Fairbairn.

He lifted out of the developing dish a wet sheet of writing paper which was absolutely blank.  Not one drop of the black ink which had recorded those sentimental effusions remained.  It was just a sheet of notepaper which had accidentally fallen into a basin of water.