

Holmes plays a defensive role, as an imperial intelligence network to detect foreigners "passing" in British society.

Imperialism, by the 1880s, had opened Europe to the peoples, cultures, and diseases of the lands it claimed. Based on Doyle's medical instructor Joe Bell, Holmes shares Koch's relentless drive to hunt down and unmask tiny invaders. In 1890, Doyle visited Berlin, where Robert Koch was testing a "cure" for tuberculosis, and in Doyle's subsequent character sketch of Koch, the scientist sounds remarkably like Sherlock Holmes. Doyle's experiences as a doctor in South Africa taught him that the colonies' microbes were his Empire's worst enemy.

Trained as a physician in the bacteriological age, Sir Arthur Conan Doyle created a detective-hero who acts both like a masterful bacteriologist and an imperial immune system.
