Presently he heard the hum of the returning aeroplane. Bob shouted as he sped by, but what he said was indistinguishable. Lawrence felt more and more despairing until with a gleam of hope he wondered whether his uncle had swum to one bank or the other and climbed to safety. He looked at the bank behind him. It was steep, almost perpendicular, but marked by fissures that promised to give him foothold. With teeth chattering and limbs trembling with cold he essayed to clamber up. At another time he would have found the feat easy enough: now he was amazed at the tax it put upon him. Every now and then he stopped, clung on with his hands, and turned his head to glance again at the stream. At last, on gaining the top, he looked along the track in both directions. Nobody was in sight. The aeroplane had again disappeared from view. Hesitating a moment he began to walk up the track. A new fear assailed him: what if the aeroplane had met with an accident! What if the engine had failed, or the pilot had been too venturesome, and in attempting to wheel in too narrow a space had crashed against the rock! Shivering as much from anxiety as from cold, he felt a glow of extravagant delight when he heard a cheery shout, and Bob came hasting towards him from round the corner of a jutting rock. "Any sign of him?" asked Bob anxiously as he met his brother. "No. What can have become of him?" "I fear the worst: but even if--if he is drowned he must come up some time. We had better walk up and down for a bit." "Where’s the machine?" "A few yards above the bridge. It was a risky thing, coming down there, but I thought I’d venture, and luckily didn’t come to grief." "Let us get our field-glasses. We can then examine every crevice in the other bank. We can’t get to the other side and examine this. By the way, how did you get across?" "One of the ropes that formed the hand-rails of the bridge is uninjured. It sags a bit, but it’s just taut enough to swing over by." For some time they marched up and down, above and below the spot where their uncle had fallen. Bob stripped to his shirt, and swam along with the current below the track, searching every cranny into which he thought the body might have been carried. No discovery rewarded his care except a primitive fishing net, the meshes of which had caught upon the jagged edges of a rock. "Do you think the Kalmucks got hold of him?" said Lawrence when they again met. "Upon my word, I had almost forgotten them. They may have done so. It’s clear that they got out of the river, and their horses, too. I didn’t see them as I flew up. What more can we do?"