At dusk a drum began to boom in the temple of the Ogrum. The sun was just on the edge of the horizon. It hung in the sky as if it hesitated to take the plunge below the rim of the world. Crouched hidden on the mountainside as near the city as he dared take his men, Craig could see the Ogrum, at the signal of the drum, start hurrying toward the temple as if they were eagerly anticipating the hellish sacrifice soon to take place. To one side, beyond the notch in the mountains, was the swamp where the dinosaurs fed. Already the sound of the great beasts fighting and screaming could be heard. All day long the Americans had remained in hiding near the city. Fortunately none of the Ogrum had ventured to climb the mountain. Craig had spent the day mercilessly rehearsing his men in the part they were to play until they were perfect in their parts, or as perfect as they could become in the short time available. The whole plan of attack depended on split-second timing. If everything worked right, if everybody did his job at the proper time, there was a chance that the attack would be successful. If anything went wrong--Craig preferred not to think about that. Around him, he could feel a tenseness creep over his men as the zero hour approached. The Ogrum, as if driven by the quickening beat of the drum, disappeared within the temple. The sun, making up its mind at last, plunged below the line of the sky. Zero hour! Craig could not see them but he knew that men had leaped from hiding and were running toward the projecting wing of the temple that formed the plane hangar. His fingers gripped the stock of the tommy-gun so tightly the knuckles showed white. They had to get that hangar, first. The planes had to be destroyed. Several times during the day he had seen planes take off. All had returned by night. The vultures were in their nest. Boom, boom-boom, BOOM, boom. Craig almost sobbed at the sound. Grenades exploding! Grenades flung into the hangar by the attacking group. Grenades blasting among the mystery planes of the Ogrum! Boom, boom, boom-boom-boom! Grenades exploding like a chain of giant firecrackers. In the hot darkness Craig caught glimpses of flashes of light as the grenades detonated. Boom, boom, boom, boom-boom! The flat sullen thuds echoed up the side of the mountain. From the darkness where the sailors crouched a low cheer arose. The men there in the night knew the meaning of those explosions. Craig held his breath, waiting. The attack was on. Now, no matter what happened, it was too late to withdraw. Now it was kill or be killed, fight or be struck down, destroy or be destroyed. With the knowledge of the savage sacrifice about to take place within the temple, there was no question of the urge of the men to destroy. The Ogrum were beyond the meaning of mercy. Blast them, mow them down, kill them, destroy them utterly!