Oh dear. I should like this. Everyone else does. The reviews say it is brilliant.
And it is indeed well-written, meticulously researched and an extraordinary piece of work.
But if I am honest I was bored. Sorry, but I was!
It depends partly on whether you can cope with history written in this sort of way:
"In 1937 James was posted to Budapest, a hotbed of international spy intrigue, where the British secret service operated a branch headed up by Lt.Col Wilfred "Squidgy" Sponge-Clibbon, who had been at school with James' father at Eton in the late 19th century when thrashings were commonplace under the headship of the notorious Major General Adolf Winterton-Snow. "Squidgy" was a spy of the old school, who drank six gins before breakfast and then spent the rest of the day asleep. But James was one of a new, eager breed of "telephonic" spies who knew how to make a phone call and were determined to use the new technology to their advantage. James was entranced by Budapest, not least by Fraulein Zsa Zsa Kratchupek's "Hot Lips" bar where all the spies would regularly meet to sell secrets over roulette. Ms Kratchupek was a colourful figure who had once drunk the Mata Hari under the table and smoked three-foot long cigars while serving drinks including exploding cocktails at the bar..."
Although admittedly it is possible my paraphrase is a tad unfair.
If you like that kind of thing, you'll love it.