The Camera Fiend by E.W. Hornung

Though he afterwards remembered a shout as well, it actually was the sound of a shot that brought the boy to his senses in Hyde Park. He opened his eyes on a dazzle of broad daylight and sparkling grass. The air was strangely keen for the amount of sunshine, the sunshine curiously rarefied, and the grass swept grey where it did not sparkle.

Pocket's first sensation was an empty stomach, and his next a heavy head into which the puzzle of his position entered by laborious steps. He was not in bed. He was not at school. He was not even under the shrub he now remembered in a mental flash which lit up all his adventures overnight. He was wandering ankle deep in the dew, towards a belt of poplars like birch-rods on the skyline, and a row of spiked palings right in front of his nose. He had walked in his sleep for the first time for years, and some one had fired a shot to wake him.