In 1913, the eminent mathematician GH Hardy received a grubby, unsolicited envelope covered in foreign stamps that contained a letter of introduction and a sheaf of idiosyncratic, occasionally incomprehensible equations. It was from Srinivasa Ramanujan, self-taught Madras shipping clerk and possessor of one of the greatest mathematical talents in history. Leavitt's fictionalised account of Ramanujan's sojourn in England during the first world war is a vividly absorbing meditation on closed worlds and open secrets (Cambridge, Bloomsbury, maleness and mathematics in general), and a probing exploration of the incommensurability of different modes of language and experience. Ramanujan was taught to sing Gilbert and Sullivan, but not told the English sleep in their beds, thus condemning him to months spent shivering atop the covers. Leavitt, however, maintains an admirable reluctance to project on to his subject, perhaps taking his cue from the mantra of one of his other characters, Wittgenstein: "What we cannot speak about we must pass over in silence".

With Keynes chattering on about cocks in one corner and Strachey moaning about the vagaries of modern transport from another, business progresses pretty much as usual for the Cambridge Apostles. On the fringes sits GH Hardy. He may be an atheist, and an emotionally cramped one at that, but Hardy achieves the sort of spiritual transcendence his more flamboyant brothers can only dream of - through mathematics. His great discovery, the Indian genius Srinivasa Ramanujan, goes further: he claims his formulae come directly from the goddess Namagiri. David Leavitt has written a clever, sensitive, gossipy account of the two men's struggles. But like Hardy, he never comes close to capturing the fascinating Ramanujan.