Think of a subject so dull that no one would possibly think to make a thriller out of it. Now double the length of said thriller. Then add the author Iain Pears - and you've got a weird magic trick on your hands.

An Instance of the Fingerpost, published more than a decade ago, was set in Oxford in the 17th century, concerning the differing viewpoints of an archivist and a cryptographer. Put like that, it sounds unpickupable. It was a triumph: a runaway success, both literary and popular.

Pears followed that with another challenging, ambitious book: The Dream of Scipio. This was based on a Neoplatonic treatise by a 5th-century bishop. I'm not making that up - Pears did. What, did he not get the “Robert Harris™” historical thriller memo, about sticking to subjects on the history GCSE curriculum, and with costumes that will look good on the BBC?

Obviously not. For Pears's latest book is based on financial systems. Not even, I hardly need add, our current credit crunch - which admittedly people are interested in, but only because they're scared they're one payslip away from homelessness. No, Stone's Fall is about the interweaving of financial, political and military systems in 1909. One cracks open the very large spine, thinking, “C'mon Iain, I know you're good, but this better be very, very, good.”

The novel, as with Fingerpost and Scipio, is told in parts, each with a different narrator and different date. We start in London in 1909, with a reporter, Matthew Braddock. He is summoned to the house of Lady Ravenscliff, the widow of the phenomenally rich John Stone. A few weeks earlier, her husband had died by falling out of the window of his office. But Lady Ravenscliff isn't interested in that. Stone declared in his will that he had a love child to whom he wanted to leave a fortune - but the papers identifying the child have been stolen. She engages Braddock in the quest.

Braddock is a listless investigator. Much of this first part is preoccupied by his study of the extent of Stone's business empire. He often complains how boring he finds it - is forever repairing to the pub for a pie and a pint and wishing he was canoodling with Lady Ravenscliff instead. Readers will probably agree.

Much the most gripping is the second part, set in Paris in 1890, and narrated by the spy Henry Cort - the stuff, in fact, of more traditional thrillers. The book ends, finally, in Venice, in 1867, with the story of Stone himself. There is barely any sex, not much action, but an awful lot of fastidiously plotted intrigue and deft period atmosphere. And, by the end, we realise that Pears has a great subject after all - not finance really, but Lady Ravenscliff, and the mystery that is woman.

Stone's Fall by Iain Pears
Jonathan Cape, £18.99; 608pp Buy the book

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