There will be more. The Second World War keeps turning up strange secrets. Macintyre, a Times writer, was alerted to Agent Zigzag, the British double agent Eddie Chapman, by a relatively bland obituary – “intriguing as much for what it did not say” – in The Times. Macintyre began the herculean task of research through archives declassified only in 2001. First, he addressed the 1,700 pages of M15’s papers: transcripts, wireless intercepts, reports, letters. Then M15 agreed to declassify more material. Macintyre worked on.

The result is an astonishing story. Macintyre traces Chapman’s antecedents as a minor conman and louche Lothario in 1930s London. After being arrested by the Nazis in occupied Jersey he joined the Third Reich’s Secret Service. He was parachuted into England in 1942, and instructed to sabotage the factory making De Havilland Mosquito planes. Instead, he turned to the British. His clandestine work continued in Norway and beyond.

If this sounds simple, Macintyre catches Chapman’s tortured complexity: “A man groping his way through moral darkness towards the light.” The psychological ambivalence is as good as anything in John le Carré. Along the way Macintyre pens some exquisite portraits. A Merchant Navy skipper: “A strong mixture of sea water, rum and rage ran in his veins . . .” Empathetic but objective, wry at times and always beautifully written, this is an admirable, absorbing work.

Agent Zigzag: Lover, Traitor, Hero, Spy by Ben Macintyre

Bloomsbury, £7.99

Buy the book here for the offer price of £7.59 (free p&p)

Times Recommends

• 10 things you should avoid in hospital (unless there really is no option)
• Exclusive: Philip Pullman's essential reading list
• The White War by Mark Thompson