Victorian London: The Sign of the Four was published in 1890, during a time when London was the largest and most influential city in the world, serving as the heart of the British Empire. The novel reflects the social, economic, and cultural conditions of Victorian London, including the stark contrasts between wealth and poverty, the rise of the middle class, and the city's status as a global hub of commerce and industry. Conan Doyle's depiction of London's foggy streets, opium dens, and bustling docks captures the city's atmosphere, reflecting both its grandeur and its darker undercurrents.

British Imperialism and Colonialism: The novel is deeply influenced by the British Empire's global reach, particularly its involvement in India. The backstory of the Agra treasure and the involvement of British officers and Indian characters reflect the complexities and moral ambiguities of colonialism. Conan Doyle's portrayal of the treasure as both a source of wealth and a cause of violence and betrayal highlights the conflicting attitudes towards the Empire and its spoils. The novel explores the consequences of British imperialism, particularly the impact on both the colonisers and the colonised, and raises questions about the ethics of empire.

Scientific Advancements and Detection: The Sign of the Four is part of the detective fiction genre, which gained popularity during the late 19th century, a time of great scientific and technological advancement. Sherlock Holmes, the novel's protagonist, embodies the ideals of rationality, observation, and deduction, reflecting the era's faith in science and reason as tools for solving problems and uncovering truth. Conan Doyle's use of forensic science and logical reasoning in the novel showcases the growing influence of scientific methods in law enforcement and society at large.

Victorian Attitudes Towards Race and the Other: The novel reflects the racial attitudes and stereotypes prevalent in Victorian Britain, particularly in its portrayal of non-European characters like Tonga. Tonga is depicted in a stereotypical and dehumanizing manner, reflecting the prejudices of the time. Conan Doyle's characterization of Tonga as a "savage" reflects the broader Victorian anxieties about race, the unknown, and the "Other," particularly in the context of the British Empire's encounters with non-European cultures. These portrayals offer insights into the racial and cultural dynamics of the period but also highlight the problematic nature of such depictions.

The Role of Women: The Sign of the Four also touches on the roles and expectations of women in Victorian society. Mary Morstan, the primary female character, is portrayed as a figure of virtue and gentility, but her role in the narrative is largely passive, reflecting the limited agency afforded to women at the time. The novel mirrors the Victorian ideal of the "angel in the house", where women are expected to be pure, submissive, and dependent on male protection. Through Mary's character, Conan Doyle provides a glimpse into the gender dynamics of the period, where women's roles were often confined to the domestic sphere.