In what is surely an early contender for 2013's Book of the Year, Lucy Ellmann once again turns the comic novel into a work of the highest art.

One might have thought after Howard Jacobson's 2010 Booker win for The Finkler Question that publishers would have saturated the market with works of comic genius. But, apart from Dan Rhodes and one or two other practitioners of the genre, comic novelists are still less highly regarded than their more serious counterparts.

There are obvious reasons for this. Humour often implies the lightweight, the superficial, the disposable. But we don't think less of Shakespeare's comedies than we do of his tragedies. Twelfth Night is as capable of, and as celebrated for, its depth and humanity quite as much as King Lear.

Indeed, it could be argued that comic writers must work harder to achieve the very depth and humanity that a serious or profoundly sad work can take almost for granted. They must be more conscious of cheap shots taken, the easy resort to the hackneyed phrase. A hyper-awareness that must masquerade as casual observation would challenge the best of us, but comic novelists carry off this trick with ease.

Ellmann's sixth novel – it is four years since her last book, Doctors And Nurses, implying that comic fiction takes every bit as long to percolate as more sombre works – is set in a kind of fairy-tale New York, where wealthy, middle-aged plastic surgeon Harrison Hanafan resides. On Christmas Eve, he slips while walking down Madison Avenue and is helped to his feet by a "plump middle-aged gal with brown eyes". In other words, by an utterly normal-looking woman who is somehow transformed into something resembling a Christmas angel. Harrison is hooked, and Mimi, as he soon discovers she is called, soon pops up in his life again.

Lest we struggle to sympathise with the plastic surgeon in his Manhattan loft apartment who has recently dumped his needy and controlling girlfriend, Gertrude, Ellmann provides a "save the cat" moment (a film term for the action an invulnerable hero must perform to show he is not quite so and thus earn our affection) as Harrison actually does save a starving cat, stuck out in the snow and soon named Bubbles for added appeal. Now he's not only limping, he's an animal-rescuing hero. We can safely adore him.

Ellmann takes us through the twists and turns of Harrison's relationship with the ever-direct and forcefully feminist Mimi, which begins when she asks him to escort her to a museum to get the rag rug her great-aunt once made returned to her (an ex-boyfriend stole it and sold it).

This is where Harrison's education begins ("Who decides what's beautiful anyway?"), and before we know it he's questioning his own profession and looking back over his childhood, and that of his sister, Bee, with fresh and rather alarmed eyes.

Can one person really change us? That's the romantic question that lies beneath Ellmann's sharp, funny, clever Manhattan tale, but instead of being a regressive or conservative question, here it is a radical one. Harrison wandered into surgery as a profession to please and impress the father who abandoned his family. Bee has devoted herself to art works that Harrison has barely registered. He phones her when he is troubled by something – this time, she is in Canterbury on an artist's residency – but otherwise, he pays her little real attention.

However, his world changes when a family disaster occurs. Events can change us as much as a person can, and Harrison finds his world shattered by a crazed gunman rampaging through the English countryside – ironically, he is a New Yorker complaining about gun violence that foreigners seem to regard generally as an American problem. Mimi has also left him after a hilarious but unhappy misunderstanding. Ultimately, though, just how much will the feminist consciousness she has exposed him to, and this family heartbreak, change him for good? And how crucial is it that they do?

Ellmann comes from a feminist family: her mother, Mary, was the author of a favourite feminist tome, Thinking About Women, and her sister, Maud, to whom the novel is dedicated, is an academic who has published work on Elizabeth Bowen and psychoanalysis. In contrast, perhaps, her father Richard Ellmann, biographer of James Joyce and Oscar Wilde, represented a more authoritative and patriarchal history. However, if Mimi is about anything, it is about family, sisters and female power, all wrapped up in a fairy tale where every word works magic to show a superlative comic novel embodying tragedy and all the human emotions. It may be Ellmann's finest novel yet.

Mimi

Lucy Ellmann

Bloomsbury, £12.99