"It's a hard nut to crack," Roque stated to a group of officers, "but I have opened just such hulls before, and I am not ready yet to plead inefficiency." "Perhaps they have fallen into the hands of the enemy," said one of the officers. "I can hardly believe that an old campaigner like Schneider would run into the lines of the foe with his eyes open. If suddenly attacked by lurking prowlers, I'll warrant we'll find some sign, for I know the man too well to believe he would be taken without a struggle and somebody biting the dust." Roque had evidently not figured on Schneider's present handicap in the shape of the boys, forcing discretion ahead of valor. Then the winning thought flashed into the mind of the secret agent--put the ambulance dogs on the trail! The reminder was the approach of one of the sanitary officers. The latter, when he was told of the situation, at first presented a doubtful front. "The heavy rains out there," said he, indicating the plain by a sweeping movement, "have drowned the scent, even if we had a good lead from this point; but," he concluded, noting the disappointment in the face of Roque, "I do not mind making a try for it. Here, Blitz." The splendid animal bounded to the side of his master, lifting expressive eyes, and indulging in a series of short barks, showing readiness to serve in the best dog language. Hasten, dog, there is sore need for aid in a dark place of yonder sea of mud! Schneider, Billy and Henri had not ventured from the ladder since the early move after the meal-bag, which the first named had decided to keep within reach, and save further wading to the shelf. The flood on the floor showed no sign of receding--indeed, the trio had twice been compelled within the hour to climb a little higher to escape the splash at their feet. Schneider, anything for diversion, pounded on the trapdoor until his knuckles were a bleeding mass, shouting until he was hoarse. "What's the use?" he dully questioned, settling again into an attitude of sullen indifference. The boys set up a duet, but with discord so apparent, even to themselves, that they quit the singing attempt as a matter of self-defense. This noise had hardly ceased, when Schneider poked his head around the ladder support on the side of the light, with a hand hollowed behind his ear. "Jumping jingo; listen!" They all heard at once the snuffing of a dog, and with the sight of its black head stuck into the bull's-eye window, Billy dropped into the flood, breast deep, and struck out for the wall, up which he swarmed, regardless of scrape or strain. He had seen the ambulance dogs in camp, and knew of the breed and their doings. Holding onto the narrow ledge like grim death with one hand, he used the other and his teeth in tearing out the scarlet lining from his cap, which he twisted around the dog's collar band. Blitz--for Blitz it was--whined his receipt for the red token, backed from the aperture, and padded away like the wind.