The Sacred Herb by Fergus Hume — Read

Here was a surprise indeed. Prelice knew that Dr. Horace had worked his way up from a humble position, and laid no claims to being of gentle blood. But he had never referred to the existence of a single relative, and the young man had always believed him to be alone in the world. Now it seemed that Agstone was his brother. And when Prelice recollected that Agstone was the same hirsute, red-haired, uncouth animal in appearance, it flashed across his mind that the brothers were twins. The extraordinary thing was that he had not noted the close resemblance before, since he had seen Agstone dead and Horace alive, within the last few hours. But the idea of connecting a common sailor with an eminent scientific man had never entered his mind.

In the cab, on the way to the New Bailey, Horace gruffly gave his companion a few facts to substantiate his statement, but Prelice observed that he said as little as he could.