The Missing Shade of Blue, By Jennie Erdal

A tale of reason, passion and the rocky road to happiness

Readers of Ghosting, Jennie Erdal's wittily astute memoir of her career as a literary double for a charismatic and capricious publisher she called "Tiger", will have wondered when, and how, she might turn such a dextrous hand to fiction. The answer comes in this "philosophical adventure", a bittersweet comedy (or comic tragedy) of ideas and emotions – and, especially, of the chronic mismatch between the two.

Set in Edinburgh and presided over by the benign ghost of David Hume, the Enlightenment philosopher and good-natured sceptic who argued that reason is - and ought to be – a slave to the passions, Erdal's novel niftily stitches ideas about happiness, sanity, memory, translation and imagination into a plot that pivots on an even more fundamental concept: love. To invoke Iris Murdoch or Michael Frayn here is not to slight the distinctiveness of Erdal's voice – merely to hint at the spread of thoughtful pleasures that await her readers.

Edgar Logan is a translator from English into French. A shy bookworm, haunted by a breakdown during his student years, he grew up in Paris with a mentally fragile Norman mother and a Scottish father who had forsaken a Cambridge college and first marriage to wed the girl who sheltered him during the war, and to run a beloved bookshop in the Latin Quarter. Edgar, one of that "lowly, benighted bunch" of translators, comes to Edinburgh to work on a French version of Hume's Essays. He swaps his Paris flat for the mews house of a philosopher in the New Town.

So he meets Harry Sanderson, another philosopher at the university: bohemian, uproarious, heretical, but "a man in crisis, unravelling before my eyes". His enigmatic wife, Carrie, is an artist from the Western Isles, her paintings full of "raw and blemished and natural" humanity.

As Edgar's friendship with this ill-assorted couple deepens, Harry the hard-drinking malcontent falls out with his despised employers, seeks solace in the patient artistry of fly-fishing, and dreams of jacking in his job to be a plumber (greeted everywhere, unlike philosophers, with "a mixture of gratitude and relief"). Through Edgar's narration, deeper layers of experience come into view: theirs, and his. With abundant humour, the novel weighs up philosophy, art and translation as rival paths to the portrayal of humanity - or even in the pursuit of happiness. "The picture is never complete – it's always lopsided or distorted in some way." We all have to translate one another, but our map of reality can only be a mosaic of fragments.

Events slide towards disaster. Madness haunts this book, just as it haunted Hume. Yet, in true Humeian style, high-spirited curiosity lends an intellectual joy even to the darkest hours. Then, in the wake of crisis, happiness dawns beside the sea in the "healing environment" of Carrie's island. Edgar voices the thought that "a good novel is like a small miracle" and can achieve "something... that could only be called truth". Hume, who didn't much care for miracles and even had doubts about truth, might have said a sceptical "amen" to that.