Catherine Gehrig is a middle-aged horologist working in "the Georgian halls" of the Swinburne Museum, London SW1. For the last 13 years she has been in love with her married colleague, Matthew Tindall, and when he dies suddenly (on 21 April 2010  the book is full of precisions) she is distraught. Out of charity and to avoid scandal, her boss Eric Croft moves her to the museum annexe in Olympia and gives her a recent acquisition to assemble: a complex mechanical toy that she first thinks might be a monkey, then decides is a duck. (Actually, it's a swan: the transformation of ugliness into beauty is one of many presiding themes.) Croft's hope is that Catherine will be led towards recovery by "the huge peace of mechanical things". In fact she is first irritated, then distracted and eventually bewitched by a story that has some peculiar parallels with her own, and some corrective deviations from it.

This story, which is told in sections that alternate with Catherine's own, involves Henry Brandling, scion of a wealthy 19th-century railway family, husband of sourpuss Hermione and father of sickly Percy. When Percy falls ill, and all the usual Victorian therapies have failed, Henry becomes convinced that a foreign and mechanical entertainment might heal him. "When my little fellow saw the design of M Vaucanson's ingenious duck," he says, "a great shout  huzza  went up from him. It was a tonic to see the colour in his cheeks, the life brimming in his eyes where I observed the 'magnetic agitation' which is a highly elevated form of curiosity or desire."

In order to turn these designs into the real thing, Henry travels to the Black Forest south of Karlsruhe, where watch-makers have a reputation for exceptional brilliance (it's the original home of the cuckoo-clock). Here he encounters assorted servants, manufacturers, schemers and dealers, before landing in Furtwangen with Frau Helga, M Artaud the silversmith and collector of fairy stories, the mechanical genius Herr Sumper, and "his golden shadow", the equally ingenious but injured boy, Carl.

While the cogs and pistons of this little society threaten to destroy Henry, rather than help him discover a means of curing his child, Catherine begins to assemble his story and the toy it centres around. It is now that parallels between the two narratives begin to emerge. Sumper, it transpires, is "a most eccentric bully" who is determined to create for Henry "something far superior" to his original desire. Croft, though less obviously manipulative, arranges for Catherine to be helped in her labours by the glamorous young Courtauld girl Amanda Snyde (Carey has always liked tell-tale Dickensian names), who is in fact a sort of spy. Her boyfriend is dead lover Matthew's elder son, and her grandfather is a friend of Croft's  and so able to pass back secrets that emerge during the reassembly of the swan.

Carey manages these time-shifts and other complications with the same easy-seeming mastery that he shows in all his novels. But here the fluency seems especially apt, because it is always devoted to the service of machines that themselves depend on being cunningly assembled and delightful. In other words, there is an immaculate fit of means with themes  although (and because) these themes turn out not simply to concern the beauty of science, but the ways in which science and humans interact and overlap.

We begin to see this all the more clearly as the story rises towards its climax, in which Sumper reveals to Henry that during his previous work-life he has been involved with a certain Sir Albert Cruickshank, a brilliant and underfunded London scientist-cum-engineer (who sounds more than a little like Charles Babbage). Carey is too subtle a writer to spell out precise meanings through this passage of bravura writing, but his intentions are clear enough. While designing the wooden patterns from which Cruickshank's greatest invention will be cast (his Mysterium Tremendum), Sumper gains an understanding of high science that is truly visionary.

Specifically, it is a vision of how to discover order in a random universe  something that runs the risk of seeming crackpot, or being proved unworkable, and yet preserves a kind of nobility. "It soon became clear to me," Henry says, "that what [Sumper] so excitably described as 'deep order' was a True Believer's attempt to give meaning to a mess  children's toys, oriental figurines, turned brass implements, fragments of marble and a huge library of books in front of almost every one of which was placed some curiosity or object, each of which beckoned one's attention." This is the lesson Catherine has to learn more than a century later. Henry pursues a beautiful invention to heal his boy; she reassembles the swan as a means of balancing her grief. In both activities, bounds are set around parts of humanity that are not mechanistic (call them "souls"  a word that appears on the final page of the novel). Yet it turns out that the most tremendous of all Mysterium Tremendums is the body, which operates according to specific laws ("the chemistry of tears"), and which suffers no loss of beauty, or wisdom  or even marvellousness  in the process.

Carey has tackled some of these ideas before (the most obvious precursor to the construction of machines in this book is the transportation of the church in Oscar and Lucinda). But here everything has been designed, tooled, oiled and fitted together with greater economy and an equal panache. Does this mean the book ends too neatly? No. Even as it settles its main concerns, it floats new ideas (was golden boy Carl the young Karl Benz?), and emphasises latent themes (the greater love between parents and children; the endless human capacity for misunderstanding).

Furthermore, its idea of order remains compellingly unstable. It is one thing to devise, like Cruickshank, a machine that accurately maps the sea-bed, so that ships don't run aground and people don't drown. It is another to devise a plan that encompasses all the moods and vagaries of humanity. In their different ways, both Henry and Catherine prove this. They know the rage for order is at once completely sensible and somewhat lunatic. Their broken hearts tell them this.

 Andrew Motion's Silver: Return to Treasure Island is published by Jonathan Cape.

Clock-making and novel-writing are  in spite of a shared need for craftsmanship  rather different activities, requiring nigh-on incompatible skills. The clockmaker deals in absolute precision, working to a design that must forgo all extraneous elements; the novelist can't afford to be so pernickety, but must always venture into the unknown, and create the impression of untrammelled life.

It might be thought hubristic for an author to draw attention to this contrast, but in his 13th novel (his 12th for adult readers), Peter Carey does exactly that. About halfway through The Chemistry of Tears, Henry Blanding, a Victorian gent with an interest in clockwork devices  who has travelled to the Black Forest, the birthplace of the cuckoo clock, to have a giant mechanical bird (it starts as a duck and ends up a swan) constructed as a "magical amusement" for his dying son  encounters a "collector of fairy tales" in the mould of the brothers Grimm, a man in whom he senses an appreciation of misery and cruelty, a tendency to see "the possibility of violence" in everything around him. The collector's presence in the narrative is conspicuous because so tangential to the plot, and it doesn't take a very donnish turn of mind to view him as a representative literary sensibility, a kind of stand-in for the novelist himself. Another difference between the writer and the clockmaker is that the writer must, as Graham Greene once put it, have a "splinter of ice in the heart", while the clockmaker can go to his trade as a refuge from difficult emotions.

Henry's narrative alternates with that of Catherine Gehrig, a horologist at the Swinburne museum in London, who has been charged with reassembling the mechanical bird a century later. These two strands of the novel are linked not only by the construction (or reconstruction) of the clockwork animal, but by their narrators' grief: Henry's son may, he fears, have died before he has a chance to present him with his gift, while Catherine is suffering after the sudden loss of her lover and colleague Matthew Tindall, a married man and father, whom she is thus forced to mourn in secret.

Carey's exceptional storytelling talents are all on prominent display here. Catherine's and Henry's voices are lustily generated and expertly distinguished from one another; contemporary London and 19th-century Germany are conveyed in lightly distributed yet powerfully evocative physical detail; both narratives are invigorated throughout by a thrilling verbal energy, and an almost unfailing knack for alighting on the mot juste (the "quarrelling" of birds at dawn, the "pulp and fibre" of the human brain). These are precisely the qualities that have always characterised Carey's novels, and which have twice made him an eminently deserving winner of the Booker prize. His perennial themes  the tension between telling a story and telling the truth; the conflicted nature of postcolonial national identity  are distinctively modern concerns, which are nicely accommodated by his trademark brand of funky, roughly vocal, charmingly deranged picaresque.

But while The Chemistry of Tears pays lip service to those themes, the main questions it poses are of a larger, more traditional, and less abstract variety  and these are less easily absorbed into the novel's form. Carey draws an explicit comparison between the clockwork automata that so fascinate Catherine and Henry and the characters themselves. Human beings are also engines, he reminds us, "intricate chemical machines"  so what accounts for our non-mechanistic attributes, our capacity for love and cruelty, rage and grief? How is it that man-made machines can be pieced back together a hundred years after they have last seen the light of day, as Catherine reassembles Henry's automaton, when he himself is lost to the passage of time? As Henry puts it in the novel's starkest passage, "What happens when we die?"

The kind of novel Carey writes  a kind in which character is intimately related to plot  is perhaps not the ideal scaffold on which to hang such grand and unanswerable questions about the soul. In Catherine's sections (perhaps because she does less adventuring than Henry), a dissonance between form and content is particularly apparent. Her grief is always described fleetingly and retrospectively  "I ran a bath I cried. I shampooed and conditioned and cried again"  without much variation, and without any attempt to inhabit the immediacy of her pain. This is a style well suited to picaresque, a mode that requires profusion of incident above depth of character, but it won't do for a novel that hopes to say something meaningful about human emotion. Catherine always seems to cry on cue; the more she does it, the less we're liable to believe in her grief. For all its brilliance, The Chemistry of Tears is a novel that speaks to the intellect rather than the heart  it is a complex and expertly crafted piece of machinery, but not an altogether convincing representation of life.