In 1938, when Bohemia and Moravia were occupied by Nazi Germany, Jaroslav and Josef Bublík left their home town of Banov to fight back. Joining the Czechoslovak Army, they fought their way to their country's exiled intelligence service in England. Jaroslav began training parachutists to go back to their home country and in 1941, Josef was amongst the first crop to be dropped. In one of the most daring and momentous actions of the Second World War, Heydrich - the Nazi 'Protector' - was assassinated. But Josef and his colleagues were tracked down in Prague and killed.

Jaroslav continued his work at the VRU - the secret wireless communication station that kept in contact with the home resistance. But in the dying days of the War, he was asked to take part in one final mission: Operation Foursquare. Sixty years later, Jaroslav's grandson wanted to know the full story. Did Jaroslav lead the last Czechoslovak parachute drop of the War? What exactly was the mission? And why had it become shrouded in secrecy?