Merivel: a man of his time, By Rose Tremain

This sequel revisits the rackety life of a 17th-century physician who can teach us new tricks

At the start of Rose Tremain's 12th novel Sir Robert Merivel, now in 1683 a settled if rather melancholy Norfolk gentleman, rescues a tattered manuscript from under his bed. In tribute to its useful if humble role, he dubs this testament "The Wedge". It bears, of course, more than a slight likeness to the account of Merivel's earlier life that, in 1989, Tremain published as Restoration.

For a novelist to revisit a favourite character (after no less than 23 years) carries risks. Besides, Tremain has from book to book always widened her horizons and deepened her repertoire. She has conjured into intense being gold prospectors in New Zealand (The Colour), Polish workers in London (The Road Home) or migrant musicians at a Baroque Danish court (Music and Silence). Her pitch-perfect virtuosity throve on changes of scene and tone quite much as her questing protagonists did.

So can the physician Merivel, that roguish and randy old dog who saw his fortunes soar, plunge and then ascend again thanks to the favour of his beloved Charles II, teach us some new tricks? Of course he can. But, even as the adventurer stirs from his estate to sample the final years of the Merry Monarch's reign (1683-1685) in full-flavoured encounters with the foppish scum of society and its destitute dregs, this novel becomes a meditation on ageing (Merivel hits his late fifties), on feelings of waste and futility, and on the search for a legacy to make a life of "Confusion and Muddle" count.

Witty and frank, with the first-person swagger of his voice as much of a treat as before, Merivel - bawdy, brazen but tender-hearted too - remains liable as ever to indulge his compassion (he saves a caged bear in France) or his lust (he kicks off an orgy in a stage-coach in the Alps). All the same, Sir Robert has to make a reckoning with posterity as - for this blithe sceptic in matters of faith - "the concept of Non-Being fills me with outrage". Merivel glimpses the sense of an ending - or rather, for this hedger of bets, of five options.

In Versailles, he fails to meet Louis XIV (with a terrific cameo of the Sun King's court as a Kafkaesque nightmare) but falls in love with a Swiss noblewoman who has a congenial passion for medicinal botany, and a conveniently gay soldier-husband. Meanwhile, his old amour Violet suffers from breast cancer. He must operate. Cue another brilliantly executed, if gory, period vignette.

Tremain gets the doctoring right, with unsparing relish but no superior hindsight - her novel has, justly, reached the shortlist of the Wellcome Prize for books with a medical theme. Merivel's dear daughter Margaret catches the King's eye and goes up to Whitehall; and he seeks to overcome a fear of "meaninglessness" via a learned treatise on the souls of animals, whose welfare always engages him.

As it bounces from one zestful set-piece to another, the novel entertains as much as its rackety hero could desire. But, like him, it also dips into sadness as thoughts of mortality tighten their grip. A weak-willed "Amalgam of vain Longings and Appetites", he wonders why his tale, or life, should matter at all. Well, as Charles himself says, "All is in the story, Merivel". For a second time, this is one to cherish.