The courage of women dropped into Nazi-occupied Europe in order to work for Special Operations Executive (SOE), was immense. Trained as spies in Britain, they were tasked with sabotage and subversion of Nazi military rule and operated covertly with Resistance fighters and other British agents. It was a hugely risky job.

Thirty-nine entered occupied France in this way, mostly by parachute. Imagining their experiences seems to be a rite of passage for many esteemed novelists – off the top of my head I can think of William Boyd, Sebastian Faulks, Simon Mawer and Kate Quinn. I have read and enjoyed their books, but there is often a sense of the protagonists being superhumanly lucky: beautiful, outspoken, brave, and able to glide through the espionage. In reality, 16 of these women were captured.

Boyd’s recommendation of this debut novel by Lori Inglis Hall was what attracted me to it. Initially, I was sceptical: the writing is lucid, evocative and accessible (no bad thing), but not extraordinary. However, I was soon hooked by a story that struck me as far more realistic than many spy novels.

Tessa and Theo are twins who have grown up in a comfortable home in Cambridge with an English lecturer father and a French mother. They have always been preternaturally close. But a wedge is driven between them when Theo senses that Tessa is keeping something from him during her last year at the Sorbonne, while he studies at Cambridge. We learn what this secret is and how it haunts Tessa for the rest of her life. But further degrees of separation inevitably develop between the twins when war breaks out. Theo joins the RAF, and Tessa – well, no one is quite sure what Tessa is doing.

In fact, she is putting her life in constant danger, working for SOE in occupied France. And here the story comes into its own. From the start, she faces immense challenges and dangers, not all of which she can overcome. It would be a spoiler to say more, but the novel takes in betrayal, duplicity, cover-ups and the effects of grief. There are no neat endings.