He peered in hastily at the other three windows. Not a soul in any one of the remaining compartments! It was a very empty train, he had noticed himself, when he had got in at Tilgate; the one solitary occupant of the front compartment of their carriage, a fat old lady with a big black bag, had bundled out at Chetwood. They were alone in the tunnel--at this end of the train at least; their sole duty now was to make haste and save themselves. He gazed overhead. The tunnel was bricked in with an arch on top. The way through in front was blocked, of course, by the fallen mass of water-logged sandstone. He glanced back towards the open mouth. A curious circumstance, half-way down to the opening, attracted at once his keen and practised eye. Strange to say, the roof at one spot was not a true arc of a circle. It bulged slightly downwards, in a flattened arch, as if some superincumbent weight were pressing hard upon it. Great heavens, what was this? Another trouble in store! He looked again, still more earnestly, and started with horror. In the twinkling of an eye, his reason told him, beyond the shadow of a doubt, what was happening at the bulge. A second fall was just about to take place close by them. Clearly there were TWO weak points m the roof of the tunnel. One had already given way in front; the other was on the very eve of giving way behind them. If it fell, they were imprisoned between two impassable walls of sand and earth. Without one instant's delay, he turned and seized his companion's hand hastily. "Quick! quick!" he cried, in a voice of eager warning. "Run, run for your life to the mouth of the tunnel! Here, come! You've only just time! It's going, it's going!" But Elma's feminine instinct worked quicker and truer than even Cyril Waring's manly reason. She didn't know why; she couldn't say how; but in that one indivisible moment of time she had taken in and grasped to the full all the varying terrors of the situation. Instead of running, however, she held back her companion with a nervous force she could never before have imagined herself capable of exerting. "Stop here," she cried authoritatively, wrenching his arm in her haste. "If you go you'll be killed. There's no time to run past. It'll be down before you're there. See, see, it's falling." Even before the words were well out of her mouth, another great crash shook the ground behind them. With a deafening roar, the tunnel gave way in a second place beyond. Dust and sand filled the air confusedly. For a minute or two all was noise and smoke and darkness. What exactly had happened neither of them could see. But now the mouth of the tunnel was blocked at either end alike, and no daylight was visible. So far as Cyril could judge, they two stood alone, in the dark and gloom, as in a narrow cell, shut in with their carriage between two solid walls of fallen earth and crumbling sandstone.