Some time later the pards could hear men coming into the laboratory and going out again. They were not in a position to see what was going on in the direction of the mill, as the laboratory shut off their view, but they gathered that the clean-up had been finished, and that the amalgam was being brought into the laboratory for Jacobs to “retort” and run down into bar-bullion. The movement of men from mill to laboratory ceased. At about the same time Bernritter and McGowan left the office and made for the laboratory. As they drew close to the building, McGowan passed on ahead and Bernritter dropped behind. The alert pards could see the super cast an upward look at one of the hills that rimmed in the valley; and, as he looked, he waved his hand. Swerving his eyes to the hilltop, Buffalo Bill caught sight of a white man’s head and shoulders just vanishing downward. “That was a signal!” whispered the scout. “The thieves are making ready for the attack.” “Hadn’t ve pedder ged oudt und ged pizzy?” champed the impatient baron. “No,” answered the scout sharply. “Don’t make a move till I give you the word. I’ll tell you what to do then, _and you do it.”_ McGowan and Bernritter could be heard entering the laboratory. An instant after their heavy footfalls had sounded on the plank floor of the small house there came sounds of a quick scramble, a sharp cry, and a heavy fall. Nomad leaped instinctively. “Wait!” breathed the scout. “Wait for the attack!” “But ther villains hev downed McGowan, Buffler!” gasped Nomad. “Undoubtedly; but they won’t add murder to their crime, if they can help it. McGowan is safe enough, for the present. I reckon that will open his eyes as to Bernritter’s character!” A tall man could be seen hurrying around the old powder-house toward the laboratory door. That was Andy O’Connell. He had heard the scuffle and the cry, and was not waiting for the mill-whistle to call him to the counter-attack. O’Connell, however, did not reach the laboratory door. Suddenly he paused and whirled about, jerking a revolver from his pocket as he did so. At the foot of the hill, where Buffalo Bill had seen the disappearing head and shoulders of Bascomb, was a pack of armed Apaches, rushing like wolves in the direction of the laboratory building. A white man was in the lead, springing over the ground with long leaps. “Nomad,” said the scout, starting up, “you and the baron will get into the laboratory building and prevent the amalgam from being taken. _Now!_” The door was flung open and the three pards rushed out. The trapper and the baron, bent only on carrying out orders, paid no attention to O’Connell or the onrushing Bascomb and his Apaches. Their business was to get into the laboratory--and they went at it. O’Connell, whirling around and seeing the three issue from the powder-house, made up his mind that they were part of the attacking-force, and had been concealed in the powder-house for no good.