With a full appreciation of the chances that he was taking he therefore let out the car to a pace which in any other circumstances he would never have attempted. Bumping over patches of loose stone, and splashing through pools of water, he held resolutely on, regardless of risk, while all the time immediately ahead of him two broad and recently imprinted tire marks stretched away encouragingly through the mud. Whatever the Inspector's private emotions may have been, it must be admitted that he faced the ordeal with masterly restraint. Once or twice, as they skidded violently round a blind corner, he caught hold of the side door with a spasmodic grip, but except for this instinctive movement he maintained an expressionless calm which certainly did credit to the self-discipline of the Yard. For the first three miles Colin needed all his skill and luck to avoid disaster; then, as they drew farther out into the lonely marshland which borders the north bank of the Thames, the conditions gradually improved. The east wind, which blows perpetually over that desolate region, had already begun to dry up the surface of the road, while with nothing but an occasional cowshed or a few leafless trees to obstruct the view, the chances of running headlong into some unforeseen death trap were reduced to much more comforting proportions. Suddenly, with an abrupt movement, the Inspector pointed ahead, to where a broad shaft of yellow light streamed out against the sky. "What's that?" he demanded, putting his lips close to Colin's ear. "Mucking Lighthouse," was the answer. "There are some powder works away to the right, and the creek they're making for is just between the two." At a furious pace the car leaped forward along the deserted road, the telltale track of the fugitives still standing out plainly in the glare of the head lamps. Colin was much too occupied with the wheel to indulge in any further attempt at conversation, while sheltering his eyes from the wind with one hand, and grasping the back of the seat with the other, the Inspector stared out in front of him in grim silence. Rounding a slight curve between two low banks, they emerged into a long stretch of almost perfectly straight roadway, and at the same moment a simultaneous shout burst from both their lips. There in the moonlight, not more than half a mile away, they could see the dark outline and gleaming tail lamp of another car, travelling swiftly in the same direction as themselves. "There they are!" roared the Inspector. "Keep her going, doctor! Keep her going, and we've got 'em!" With an inward prayer that his tires would stand the strain, Colin drove down the accelerator to its extreme limit. The well-tuned engine responded to his call, and with the wind rushing in their faces, and the whole chassis quivering and rocking beneath them, they surged on recklessly in pursuit of their escaping quarry.