James McCarthy's Gun

James McCarthy's Gun is a pivotal piece of evidence in 'A Study in Scarlet,' the second novel in the Sherlock Holmes series published as part of its foundational stories, where it plays a crucial role in unraveling the mystery surrounding John Hatherley's murder. The revolver, found near the crime scene with its last cartridge discharged, initially implicates young James McCarthy but is ultimately exonerated by Holmes as belonging to the true culprit, John Ferrier. Across the broader series, the gun does not reappear or evolve further, remaining a one-off artifact emblematic of Holmes' deductive prowess in distinguishing innocence from guilt.