The reader has already learned of the decision reached by Harold Leighton and David to visit Bogota in order to solve there the mystery of the three months following the dynamite explosion in the Guatavita tunnel. As her uncle had foreseen, Una insisted on going with them, and had brought Mrs. Quayle along besides. There was no particular reason why that estimable lady should accompany them. She had rarely ventured beyond the borders of her native Connecticut, and could certainly be of no possible use on so long and difficult a journey as this. But something had to be done with her. She was afraid to be left alone at Stoneleigh, and as she was anxious about Una it seemed best on the whole to take her along. She proved an inoffensive traveler and gave amusement to more than one tourist by her extraordinary costumes, especially the massive, old-fashioned jewelry, with which her hands and neck were covered and from which she refused ever to be parted. The trip was a hard one for Leighton, who was wedded to his quiet methodical life in Rysdale, and who had no mind for the distractions and annoyances of foreign travel. He was spurred to activity, however, by his interest in the psychological puzzle presented by David, added to which was a growing curiosity regarding the mysterious Indian lake and its reputed treasure. An ordinary mining scheme, no matter how promising, would not have moved the philosophic master of Stoneleigh. But here was something out of which might come a fine scientific discovery revealing the secrets of a bygone civilization. Hence, he had not regretted his resolution to make this quixotic pilgrimage and, as he had latterly fallen into a sort of dependence on Andrew Parmelee for much of the detail work connected with his scientific studies, he had arranged with the village authorities for the schoolmaster to accompany him to Colombia. Andrew was not a little alarmed at the intimate daily association with Una, the object of his adoration, which such a journey involved. But the fancied terrors of the situation had their compensations. It might even happen that in the primitive region to which they were going he could be of vital service to this stony-hearted fair one--a possibility that filled him with dreams of deadly peril by land and sea in which he acted the part of rescuer to helpless innocence. So, this modern knight errant was miraculously strengthened to ward off the attacks of his Aunt Hepzibah, and departed on his mission fired with all the zeal of the hero of La Mancha, his high resolve unclouded by the horrors that speedily came to him in the rotund nightmare known in the flesh as Doctor Miranda. "Ah, this little Yankee," repeatedly declared that restless follower of Aesculapius, regarding the bewildered Andrew with professional glee; "he must take my pills or he will die!"