When the Bosnian Serb Gavrilo Princip assassinated the heir to the Austrian throne in Sarajevo in 1914, he was just short of his twentieth birthday. He was to spend the next four years in the garrison prison in Terezín and this was where he died. The little-known story of his forced stay in what is now the Czech Republic was the inspiration for the latest novel by the British writer, David Whiteman.