We are in the South Tyrol, the anomalous part of Italy where the people speak German and the surroundings look more like Austria: "the wide wooden balconies, the Gothic script over shops and hotels . . . the little children in lederhosen, the onion domes of the churches".

Clive, a globe-trotting beardie, and his Italian girlfriend Michela, as a break from protesting against climate change, the G8, the World Trade Organisation and all that, have organised a kayaking school to take advantage of the region's snow-fed rivers, which are especially lively this summer as global warming melts the Alpine glaciers. The school's first group consists of four adults and nine kids from Kent. Clive knows some of them through Waterworld, a leisure facility in those parts.

So they all paddle about in the rushing white waters, perform feats of skill, make foolish mistakes and, in the evenings, develop personal conflicts. Keith, the jolly group leader, makes everybody stand up and say a few words about themselves on the first night. With a large cast it can be difficult to remember who everybody is, so Tim Parks has probably included this as something to which we can refer back.

Two of the group stand out a little. Vince, a recently widowed banker accompanying his teenage daughter, arrives by car, not by minibus with the rest, and a scene set en route gives us some of his thoughts and feelings. Eventually he will emerge as the central character, though it takes a while. Adam (oh dear, I had to look his name up in the scene of Keith's bonding session) is always described as "the chinless man", so his image, at any rate, sinks in. He has brought his son, leaving his bedridden wife at home but constantly texting her on his mobile - another mnemonic device.

Adam is possibly an accountant, but I cannot now find the passage that tells you. More importantly, he is a part-time instructor at Waterworld, as was Vince's late wife, and Vince suspects they may have had an affair on a previous expedition to the Ardeche, or "Ardeche", as Parks and his editor always manage to mispunctuate it. Vince, however, realises his jealousy may be irrational and no needling ensues. It is Adam and Clive who have a huge row.

Clive is sounding off pompously at the ever-reasonable Vince about the evils of third world debt when dry-stick Adam suggests that despite Clive's big talk of saving the planet, all he actually does is run a "little business in the tourist trade", so Clive hits him. "As in a collision on the road there was a split second in which everybody realised that they were involved in some kind of accident, without yet knowing how serious." Parks is very good on people's reactions, in all kinds of circumstances.

As things turn out, the next time Clive goes on a demo, it will be of a dramatic and potentially self-sacrificial nature. Perhaps because of this, he has stopped sleeping with Michela. His only explanation is that the world is not a fit place for love, though we will later surmise that he does not want her to miss him too much when he goes. Not knowing the score, she is simply furious and heartbroken. She decides to sleep with one of the boys in revenge, which then makes one of the girls equally furious. All round, not really the ideal atmosphere in which to pursue a dangerous sport, where lives can depend on everybody looking out for each other. And Keith, the genial peacemaker, has already had an accident, his arm is in a sling and he is not there when the group makes its climac- tic trip on the deadliest rapids of all.

The social dynamics, then, are intriguing and well handled, and the many descriptions of wild waters and advanced kayaking techniques are very effective. A curious feature of the novel, though, is that it seems to come to its natural end about two-thirds of the way through, as the expedition concludes, and one wonders what the remaining wad of pages can be all about. The story then goes off at a tangent and deals specifically with Vince's mid-life crisis, which is only now revealed as the real point of the thing.

The reader's rapt interest continues, but the overall shape is a little awkward. And there is a certain flirtation with cliche: Vince, as a token of his resolve to move on, throws his wedding ring in the river, like the big jewel that you just know the heroine of Titanic will end up chucking in the sea. The closing scenes appeal to middle-aged male fantasies, not too brazenly, but detectably. Plenty of money, fresh start, exotic young totty - despite the spare, subtle, crafted prose and the modish environmental awareness, somebody is ticking some good old-fashioned boxes.