In foggy November 1880, Mr. Alistair Vance of Lloyd’s of London seeks Sherlock Holmes’s aid. The 400-ton brigantine The Northern Star allegedly foundered off the Isle of Wight, prompting a £35,000 insurance claim. However, British naval patrols recently intercepted a Portuguese schooner carrying missing government-marked Martini-Henry rifles—weapons stolen from an Ordnance barge bound for Transvaal Boer insurgents on the eve of the First Boer War. Analyzing ship ledgers, Holmes notices the Northern Star drew far less water than a vessel carrying heavy machinery should, proving she left London loaded with light ballast. She rendezvoused at Gravesend to take on 2,000 illicit rifles. Holmes and Watson trace the conspiracy down the Thames into Limehouse’s shadowy docks, untangling a web of murdered dockworkers and altered customs manifests. They uncover a dual plot engineered by shipping magnate Sir Arthur Pendelton and Captain Nathaniel Scupper: collect a colossal insurance payout on a "sunk" ship while secretly smuggling arms to South Africa. The conspirators scuttled a decoy vessel near the treacherous Goodwin Sands, while repainting and reregistering the original ship as The Vanguard. Tracing missing rifle serial numbers back to a BSA gunsmith in Birmingham and deciphering telegraph ciphers between London and Antwerp, Holmes pinpoints Pendelton’s location. In a tense midnight climax off the Dorset coast, Holmes, Watson, and an Admiralty launch intercept The Vanguard during a ship-to-ship arms transfer. After a sharp skirmish on the Channel waters, Pendelton is arrested, the rifles are secured, and British diplomatic neutrality in South Africa is preserved. Back at Baker Street, Holmes closes another successful case, having untangled a web of maritime fraud, murder, and high-stakes international treason.