While fictionalised, many of the events and characters in the book are grounded in real history.
Gandhi did call for non-violent, non-cooperation with the aim of independence by the end of 1921, and amid the turmoil, the British government really did send Prince Edward, later King Edward VIII, who married Mrs Wallis Simpson and then abdicated, on a goodwill tour. Chitta Ranjan Das was indeed Gandhi’s chief lieutenant in Bengal, and Subhash Bose, a man who would later go on to be a nationalist hero, had recently returned from England and become Das’s deputy.
Das’s wife, Basanti Devi, did speak to a rally in place of her husband and was duly arrested by the authorities, thereby re-energising the flagging non-cooperation movement.
Porton Down has, for over a hundred years, been the home of the UK Ministry of Defence’s science and technology laboratory. Their scientists, as they were later to do with British and Australian troops, did carry out biological tests, including mustard gas experiments, on unsuspecting Indian troops, though these experiments took place mostly during the 1930s rather than during the First World War. The clandestine tests were carried out at a facility in the city of Rawalpindi, now in Pakistan. Anyone interested in reading more on the subject could do no better than to start by tracking down a copy of Gassed: British Chemical Warfare Experiments on Humans at Porton Down by the journalist Rob Evans.