The Black Gang by H.C. McNeile

Two things saved Drummond from what was practically certain death -- the heavy coat he was wearing, and the fact that he rolled sideways clear of the steering wheel as soon as the man let go of him with his hand. Had he remained behind the wheel he must infallibly have gone to the bottom with the car, and at that point where the river narrowed to come through the piers of the bridge the water was over twenty feet deep. He had sufficient presence of mind to take a deep breath as the car shot downwards; then he felt the water close over his head. And if before his struggles to move had been fierce -- now that the end seemed at hand they became desperate. The desire to get clear -- to give one kick with his legs and come to the surface roused him to one superhuman effort. He felt as if the huge heave he gave with his legs against the floorboards must send him flying to the top; afterwards he realized that this vast effort had been purely mental -- the actual physical result had been practically negligible. But not quite, it had done something, and the coat did the rest.

With that one last supreme throw for life his mind had overcome the effects of the poison to the extent of forcing his legs to give one spasmodic little kick. He floated clear of the car, and slowly -- how slowly only his bursting lungs could testify -- the big coat brought him to the surface. For a moment or two he could do nothing save draw in deep gulps of air; then he realized that the danger was not yet past. For he couldn't shout, he could do nothing save float and drift, and the current had carried him clear of the bridge out of sight of those on top. And his mind was quite clear enough to realize that the coat which had saved him, once it became sodden would just as surely drown him.