Interregnum offers an alternative history of the country’s-and Winston Churchill’s-finest hour.

1. Britain is occupied by Nazi Germany. All seems lost-until the February Rising sees off Hitler. The Fuhrer’s death triggers a struggle for power among the Nazis, revolt across the Occupied Continent, and schism in the Oval Office in Washington.

Caught in this maelstrom are the teenage princesses Elizabeth and Margaret. For Churchill, what price the lives of the two women, first and second in line to the throne, weighed against the threat of an atom bomb poised to destroy New York?

There’s a Tolstoyan cast including the princesses themselves, their uncle Edward VIII, Wallis Simpson, President Roosevelt, the Kennedy family and sundry Air Chief Marshals, Field Marshals and First Sea Lords.

As to the plot, this triple-decked thriller, detective story and literary Ludo keeps its readers guessing until the very last word.