Themes & patterns

Holmes's use of cocaine to escape mental stagnation and his alternating moods of elation and black depression highlight how his relentless pursuit of intellectual stimulation leads to self-destructive habits and emotional instability.

Jonathan Small's story reveals a conflict between legal justice and personal vengeance, as he feels the Agra treasure is rightfully his after years of suffering, and he destroys it rather than let it go to those he deems undeserving.

The Agra treasure drives greed, betrayal, and murder, from Major Sholto's avarice in withholding it to the violent deaths it causes, ultimately leading to its destruction as a symbol of its poisonous effect.

The story's backdrop of British India, the exploitation of native servants, and the brutal treatment of convicts like Jonathan Small reflect the moral complexities and injustices of the British Empire.

Holmes's cold, analytical approach to detection contrasts with Watson's romantic feelings for Mary Morstan, illustrating a tension between logical deduction and human emotion, with Holmes criticizing Watson for 'tinging' detection with romance.

Mary Morstan's position as a governess with limited means, Watson's self-consciousness about his modest income, and the contrast between the Sholtos' luxury and the squalid settings highlight Victorian class divisions and aspirations.

The bond between Holmes and Watson is tested through danger and moral dilemmas, while the 'Sign of Four' pact among Small and his companions demonstrates loyalty twisted by criminal intent.

Despite Holmes's brilliant deductions, the treasure is ultimately lost and the case ends ambiguously, suggesting that even the most rational methods cannot always achieve perfect justice or resolution.