The Fellowship of the Frog by Edgar Wallace

There was no detective in the world who looked less like a police officer, and a clever police officer, than Elk. He was tall and thin, and a slight stoop accentuated his weediness. His clothes seemed ill-fitting, and hung upon rather than fitted him. His dark, cadaverous face was set permanently in an expression of the deepest gloom, and few had ever seen him smile. His superiors found him generally a depressing influence, for his outlook on life was prejudiced and apparently embittered by his failure to secure promotion. Faulty education stood in his way here. Ten times he had come up for examination, and ten times he had failed, invariably in the same subject--history.

Dick, who knew him better than his immediate chiefs, guessed that these failures did not worry Mr. Elk as much as people thought. Indeed, he often detected a glum pride in his inability to remember historical dates, and once, in a moment of astonishing confidence, Elk had confessed that promotion would be an embarrassment to a man of his limited educational attainments. For Elk's everyday English was one of his weaknesses.