The Kingdom of the Blind by E. Phillips Oppenheim

Surgeon-Major Thomson reeled for a moment and caught at the paling by his side. Then he recovered himself almost as quickly, and, leaning forward, gazed eagerly at the long, grey racing-car which was already passing Buckingham Palace and almost out of sight in the slight morning fog. There was a very small cloud of white smoke drifting away into space, and a faint smell of gunpowder in the air. He felt his cheek and, withdrawing his fingers, gazed at them with a little nervous laugh -- they were wet with blood.

He looked up and down the broad pathway. For nine o'clock in the morning the Birdcage Walk was marvellously deserted. A girl, however, who had been driving a small car very slowly on the other side of the road, suddenly swung across, drew up by the kerb and leaned towards him.