On 19 April 1949, the Royal Navy
frigate HMS
Amethyst sails up the
Yangtze River on her way to
Nanjing, the Chinese capital, to deliver supplies to the British Embassy. Suddenly, without warning,
People's Liberation Army (PLA) shore batteries open fire and, after a heavy engagement,
Amethyst lies grounded in the mud and badly damaged. attempts to tow
Amethyst off the mud bank, but is herself hit several times and has to depart. A further rescue attempt by
HMS London in consort with
HMS Black Swan also comes under heavy fire and has to be aborted. Fifty-four of
Amethysts crew are dead, dying or seriously wounded, while others deteriorate from the tropical heat and the lack of essential medicines, including the ship's captain, who dies of his wounds. An attempt to evacuate the wounded is only partially successful – the officers of the
Amethyst become aware that two seamen have been captured by the PLA and are being held at a nearby military hospital. Lieutenant-Commander
John Kerans (
Richard Todd), assistant
naval attaché in nearby Nanjing, is ordered to go to the beleaguered ship and take command. Kerans decides to risk steaming down the Yangtze at night without a pilot or suitable charts. Before they can leave, however, the local PLA
commissar Colonel Peng (
Akim Tamiroff) makes contact with the
Amethyst and at a meeting between senior officers makes his position clear: either the British government releases an apology accepting all responsibility for the entire incident, or the
Amethyst will remain his prisoner. Similarly, he will not allow the two wounded sailors to leave unless they give him statements declaring the British to have been the transgressors, which they refuse to do. Kerans dismisses his demands but is able to manipulate Peng into the release of the seamen; meanwhile, as talks progress he has the ship patched up and its engines restored. After some subtle alterations to the ship's outline to try to disguise her,
Amethyst slips her cable and heads downriver in the dark following a local merchant ship, which
Amethyst uses to show the way through the shoals and distract the PLA. When the shore batteries finally notice the frigate escaping downriver, the merchantman receives the brunt of the PLA artillery and catches fire, while
Amethyst presses on at top speed. Encountering an obstruction in the river in the form of several sunken ships, and having no proper equipment for charting a safe course, Kerans uses both intuition and luck to slip through before then reaching the guns and searchlights of
Woosung. After she is inevitably spotted, the
Amethyst is forced into a lengthy fight with the PLA batteries as she flees with all guns blazing, heading for the mouth of the river just beyond. As day dawns, she finally reaches the open ocean, where she greets with the message "Never – repeat never – has another ship been more welcome". She also sends a signal to headquarters: "Have rejoined the fleet south of Woosung ... No major damage... No casualties....God save the King!" The film then ends with scrolling text reciting verbatim the message sent the very same day from King
George VI, commending the crew for their "courage, skill and determination". ==Cast==