This is the story of Ursula Kuczynski, a Soviet spy who was instrumental in ensuring that Stalin was able to build an atomic bomb. So at first glance, not an entirely sympathetic character. And yet in Ben MacIntyre’s hands, one cannot help but admire her.

Ursula was born into a middle-class German Jewish family in Berlin. She joined the Communist Party in the 1920s, participating in street battles with the police. For the first two decades of her work as an agent of Soviet military intelligence (the GRU) she devoted herself to the struggle against fascism. She served the cause in China, Poland, Switzerland and finally in a small village in Oxfordshire, where she was known as “Mrs Burton”. During her time in Switzerland, she plotted with other agents to kill Hitler. It was a good plan and might have worked, but was scuppered by the Hitler-Stalin pact. She was never caught, and eventually fled with her children to East Germany where she died in 2000.

Though she remained a Stalinist her entire life, and was bitterly disappointed when the German Democratic Republic came to an end, there is much to be admired in her work, especially in the early years.

Ben MacIntyre is a brilliant writer and tells Ursula’s story with compassion and understanding. He does not minimise the horrors of the Stalin regime (Ursula’s first husband, also a Soviet spy, spent years in the Gulag).

After reading this book, I wonder why I ever bother to read espionage fiction. The real thing is so much better.