He returned after an hour. In the morning a man would be found bound and gagged, with five hundred pesos stuffed into his pockets. His boat would have vanished. But there was a commotion before the house where Paula waited fearfully. A carriage stood there, with a company of mounted soldiers about it. Someone was being put into it. As Bell broke into a run toward the house the carriage started up and the soldiers trotted after it. Paula was taken. CHAPTER XIII That night Bell turned burglar. To attempt a rescue of Paula was simply out of the question. He was entirely aware that he would be expected to do just such a thing, and that it would be adequately guarded against. Therefore he prepared for a much more desperate enterprise by burglarizing a bookstore in the particularly neat method in which members of The Trade are instructed. The method was invented by a member of The Trade who was an ex-cabinet maker, and who perished disreputably. He killed a certain courier of a certain foreign government, thereby preventing a minor war and irritating two governments excessively, and was hanged. The method, of course, is simplicity itself. One removes the small nails which hold the molding of a door panel in place. The molding comes out. So does the panel. One enters through the panel, commits one's burglary, and comes out, replacing the molding and the nails with reasonable care. Depending upon the care with which the replacing is done, the means of entrance is more or less undiscoverable. But it is usually used when it is not intended that the burglary ever be discussed. Bell abstracted two books, wrapping paper and twine. He departed, using great care. He walked three miles out of town and to the banks of the Paraguay. There he carefully saturated the pages of both books in water, carefully keeping the bindings from being wetted. Then he tore one book to pieces, saving the leaves and inserting them between the leaves of the other book. Then, with a brazil nut candle for illumination, he began to write. * * * * * You see, when two thoroughly wetted pieces of paper are placed one above the other with a hard surface such as the cover of another book under them, you can write upon the top one with a stick. The writing will show dark against the gray of the saturated paper. You then remove the top sheet and end the writing reproduced on the bottom sheet. And then you can dry the second sheet and find the marking vanished--until it is wetted again. It is, in fact, a method of water-marking paper. And it is the simplest of all methods of invisible writing.