The island of Gaillardia is an ex-British colony, accidentally discovered in 1720 and finally granted self-government some 200 years later due to the interminable civil war between its north and south. The British government's resident adviser, who was never informed that he should have returned to England in 1916, reports that the island has recently become the site of Russian mining operations.
During an investigation - under the guise of a British Council cultural visit - the Gaillardian king is assassinated while watching a display of Morris Dancing, and his son ascends to the throne. Though raised in Britain and educated at Oxford, the young King is thought to be susceptible to alliance with the Russians, so Cadogan De Vere Carlton-Browne, head of the Foreign Office's Miscellaneous Territories department, is despatched to Gaillardia to strengthen ancient British ties.
The young King is resident in the northern half of the island, while his uncle, the Grand Duke Alexis, is said to be arming himself in the south. The King refuses to co-operate with Carlton-Browne, and intends to find out what interests Britain and Russia have in Gaillardia, with the ultimate aim of improving conditions for his impoverished people. Meanwhile , his duplicitous Prime Minister, Amphibulos, sees the situation as an opportunity to play the powers off against each other for his own financial gain. On a visit to the north, Alexis demands that the King abdicate in favour of the Princess Ilyena.
The King decides that a show of strength is necessary, but a planned military display reveals his armed forces to be embarrassingly depleted, and the event becomes even more of a disaster when the podium on which the guests are seated collapses. With all the major powers now mining on the island, and the Grand Duke's army advancing to the north, the British government decides to take drastic action. A policy of partition is unanimously approved by the United Nations, and a dividing line is painted across the middle of the island.
The King is invited to London for a meeting with the Foreign Secretary, and demands the return of the other half of his island. British mineralogists report that deposits of cobalt have been found; these would facilitate the construction of the hydrogen bomb, but are on the south side of Gaillardia, over which the UK no longer has any control. The King is therefore kept waiting for two weeks while Alexis is brought over for negotiations with the government.
Alexis, who is secretly also in league with Amphibulos, hopes to use Ilyena as a pawn in the deal by marrying her into British society. When she discovers this, she storms out and meets up with the King, who has been equally infuriated to discover the presence of Alexis. They go dancing together and agree to become allies.
Everyone returns to Gaillardia, where revolution has now broken out. British troops are sent in, and the government proposes to the UN that the partition be lifted. This time, however, Russia votes against the motion and sends troops to support the revolution.
Carlton-Browne is sent back to Gaillardia to deal with the situation and, after an abortive exercise in which British troops surround their own headquarters, he is captured by the King's counter-revolutionaries. The King reveals that Alexis' forces are on the brink of defeat, and that he and Princess Ilyena are to be married, finally uniting north and south.
Alexis and Amphibulos are exiled to Portugal, while Carlton-Browne receives both Gaillardia's highest honour and a knighthood for services to world peace and British diplomacy.
