Justin makes his journeys like a kind of holy rogue agent, picking his way through shady commercial deals, government collusion and outright corruption as if he were on a latterday Pilgrim's Progress. There is much up-to-date business with computers here, including a neat twist with a virus. And these aren't the only territories where classic le Carré tropes of betrayal and counter-betrayal can be turned and turned again. It is, however, mostly Justin's ghost-talking that we listen to, as his quest takes him to Elba (home of Tessa's Italian family), northern Germany, central Canada and south Sudan. The interior monologue of that passage is very typical of the way le Carré will let us have a bit of each character without losing his main focus. Are you lying on your bed flailing yourself in the darkness? Or are you staring through your bars into the garden, talking to her ghost?' Now his own wife Gloria has taken a fancy to the grieving adult schoolboy (for so Justin initially seems) hiding in their guest suite: 'What are you doing down there? she wondered. A slug of a man who used to ogle the beautiful Tessa, Sandy even sent her a love note in a moment of weakness. At first Justin simply hides out in the house of one such, the very same Sandy.

It turns out that diffidence can be a powerful attribute when you are surrounded by scoundrels. As his colleague Sandy Woodrow puts it to the pair of British police who come over to investigate the murder, Justin 'loves nothing better than toiling in the flowerbeds on a Saturday afternoon - a gentleman, whatever that means - the right sort of Etonian, courteous to a fault. Handsome, diffident Justin (the 'constant gardener' of the title) at first appears not quite up to the task of tracking down her killers. You? she is blowing stupidly as they kill her, her mouth formed into an oo.

Her husband Justin, also First Secretary at the High Commission, is faced with identifying her severed head: 'Her eyes closed and eyebrows raised and mouth open in lolling disbelief, black blood caked inside as if she'd had all her teeth pulled at the same time. John le Carré's latest novel does just that, as news comes to the British High Commission in Nairobi that human-rights activist Tessa Quayle has been murdered - butchered - up in northern Kenya. In medias res is where they say you should always start.

Le carre the constant gardener