Deception and intrigue are common elements featured in many works of detective fiction, which allow the events of the plot to unfold in surprising, unexpected ways. The Sign of the Four is no exception, and Conan Doyle employs these methods regularly throughout the narrative, providing layers of truth and lies for Holmes and his companions to navigate. Circling out from a betrayal many years prior, Jonathan Small’s complex machinations soon involve unwitting players such as Mary Morstan and the Sholto brothers. Their involvement invites more questions than answers, and their journey to uncover the secrets of their fathers leads them through layers of half-truths and misunderstandings. 

Small, a man whose life was upended when attacked by Indian rebels who forced him to steal a treasure belonging to the rajah, eventually explains the decade-long conflict that drove him to act as he does. Captured by Holmes’s clever deductions, the man reveals all. Human greed, revenge, and justice spiral into his narrative, integrated into Conan Doyle’s nuanced mystery. The pieces fall into place and, as any work of detective fiction, all is laid bare to reveal the truth that spent so long obscured. 

Written in 1890 at the height of the British Raj’s direct rule over colonial India, The Sign of Four offers many representations of Indian people, though these images are generally inaccurate and steeped in the author’s subjectivity. Though Conan Doyle was a relatively progressive writer, he represents non-Westerners as lesser subordinates. By 1890, Britain had spent decades in India, and after an 1857 bid for independence by Indian rebels, established a secure structure that would oversee the nation until 1947. Conan Doyle uses this historical backdrop to situate his 1890 novel, as Mary Morstan’s father was an officer in the Indian regiment, and his time in India is what sparks Mary Morstan’s—and by extension, Holmes's—exposure to the subcontinent and its mysteries.

At no point does Conan Doyle comment on the morality of his nation’s actions in India. Instead, he descends into caricature and misrepresentation, as in the case of Thaddeus Solto’s Indian servant, who calls him Sahib, meaning “master.” Conan Doyle describes the servant as "clad in a yellow turban, white loose-fitting clothes, and a yellow sash.” His description continues as he comments: "there was something strangely incongruous in this Oriental figure framed in the commonplace door-way of a third-rate suburban dwelling-house." Conan Doyle explicitly avows here that "Hindoos" are unsophisticated and so out of place in Western (British) environments. Later, when Holmes enlists the help of the "Baker Street Irregulars," the foreign boys are described as "dirty and ragged little street-Arabs." Finally, the fact that Tonga is responsible for the murder of Bartholomew Solto allows a foreigner to take the fall for a crime that would otherwise be on the hands of an Englishman. The colonial culture of Conan Doyle’s contemporary environment seep into the pages of his novel. Consequently, The Sign of Four projects a decidedly racist and eurocentric air.

Much of The Sign of Four focuses on the various attempts to right injustice. Mary Morstan comes to Sherlock Holmes with a letter that says she has been treated unjustly and which calls her a "wronged woman." As Thaddeus Sholto later explains, his father, Major John Sholto, has kept Mary's father's death a secret from her for ten years and "withheld from her the treasure" she was supposed to have. Thaddeus wants to give Mary her part of the treasure, but then it is stolen. The pure Mary is the wronged innocent whose rights Sherlock Holmes hopes to defend by discovering the whereabouts of the fortune. Beyond Mary, who is entirely innocent, the novel hinges on betrayal and revenge. Small seeks to find the treasure he feels is rightfully his. He seeks to reconcile the lifetime he spent in penal colony, betrayed by Sholto, but, in so doing, realizes that justice has escaped him. Nothing can resolve the sins of the past, and he has wasted his life pursuing a cold and empty prize.