Despite how they’re depicted in the movies, spies are often the last people you’d expect them to be. Never has that been truer than in the case of the subject of the upcoming film, Red Joan: Melita Norwood, the KGB’s longest-serving British spy.

For 40 years, Norwood secretly passed information to the Soviet Union about Britain’s nuclear capability. Only when she was a widowed octogenarian living out her final years in Bexleyheath, did the authorities finally discover what she’d been up to.

Working as a secretary at the British Non-Ferrous Metals Research Association, a pivotal organization dedicated to the development of nuclear weapons, Norwood was able to pass on sensitive information to the Soviets whilst being overlooked by her superiors.

Now, a film inspired by her story is coming to the big screen. Judi Dench and Sophie Cookson share the role of Joan, a character whose life is based upon Norwood’s. Dench portrays Joan's older self, after she has been found out. The film then flashes back to her younger years, with Sophie Cookson in the role as we see how Joan became radicalized.

Neither Dench nor Cookson are a stranger to the world of spies. Dench made the role of M her own in the James Bond series. Meanwhile, Cookson played Roxy in both Kingsman: The Secret Service and its sequel The Golden Circle. This time, though, they’re both on the opposite side, which should provide compelling performances as the underestimated Joan.

Based on a shocking true story, Red Joan won't be your usual spy film. Keep an eye out when it's released in cinemas on 19 April.