In this episode, one of Britain's far-flung outposts is in danger. Only one man can restore the situation—Lieutenant Harry Seagoon, who leaves post-haste for the besieged Fort Thud (close to the frontier of Waziristan) with the plans of a Union Jack in his pocket. However, the Fort has been built on shifting sands and is traveling north at the rate of twenty miles a day. The story humorously explores what happens when the Fort crosses the frontier into Waziristan.