The Man Who Forgot His Wife, By John O'Farrell

John O'Farrell's fourth novel is a tale of laughter and forgetting. Its hero, a teacher, husband and father called Jack Vaughan, is on the Tube when he realises that he doesn't know where he is. More worryingly, Vaughan doesn't know who, what, when or, more to the point, why he is either. Checking himself into hospital, he learns that he has suffered a "psychogenic fugue" – not a piece of avant-garde music but the sort of amnesia that is a staple of high-concept narratives from Memento to S J Watson's Before I Go to Sleep.

What Vaughan has not mislaid is his desire to crack a joke. Hoping to jog his errant memory, he reads a book of baby names, only to find the plot unsatisfying: "Aaron ... has a walk-on part right at the beginning but then we never hear from him again." This follows a more obvious gag about Vaughan's possible criminal past: could his felonies include "paedophile", "vivisectionist" and "banker"? Boom-boom.

Vaughan is informed that most psychogenic fugues are the result of severe psychic trauma. As he begins his recovery, however, we see that absent-mindedness is not a new condition but something like Vaughan's permanent state of mind. Distracted by routine and disillusioned by the modern world, he has become unmoored from his founding passions: why he became a history teacher, for example.

More grievously, Vaughan has lost the loving feeling that glued him to his wife, Maddy. Indeed, the largest missing piece of his existential jigsaw is the fact that Maddy has filed for divorce and is dating a smarm-bomb called Ralph. Could that explain the pesky fugue? The neat twist is that when Vaughan meets Maddy to finalise the divorce, he falls head-over-heels in love at "first" sight, so a voyage of self-discovery doubles as romantic quest to win her back.

O'Farrell has played this tune before. The Man Who Forgot His Wife remixes his very funny debut The Best a Man Can Get. Both feature complacent, mildly flawed middle-aged heroes who take their lives and loves for granted. Both men have charming, lively families – even their children, Alfie/Jamie and Millie/Dillie, sound similar. And both conduct their soul-searching while underwater in the bath.

This last is a telling image. Beneath Vaughan's bubbly, if occasionally tiring stand-up routines lurk deeper meditations on the perils and compensations of ageing. O'Farrell's amnesia plot device catches that eerie sensation of looking in the mirror and failing to recognise the grizzled old goat staring back.

Vaughan's predicament raises fundamental questions, even if in a light-hearted form. Are we simply the sum of our memories? If our slate was wiped clean, could we, like Vaughan, be transformed from self-centred curmudgeons into thoughtful liberals with awkward sexual techniques? But O'Farrell himself would doubtless mock this sort of thing out of existence. His one-liners aim to entertain, puncturing moments that come close to philosophy or sentimentality.

Indeed, what elevates O'Farrell's fourth novel above his first is that its comic routines are imbued with emotion. The Best a Man Can Get felt like a witty series of sketches stitched into a narrative. The Man Who Forgot His Wife is a coherent story told through character, humour and pathos. The furious argument between Vaughan and Maddy that is preserved on a family home movie is believably excruciating. A running joke involving a postcard of a cartoon leprechaun is touching and skilfully deployed. The scenes involving Vaughan's seriously ill father are poignant and funny: I don't want to spoil the punchline on page 106, but the phrase "Who fuck hell are you, fuck-bastard?" deserves its own game show.

Not everything works. Witness the images of tents collapsing allegorically. (Like a relationship they need two poles to stay up.) The brief attempt to explore history isn't any more convincing than it was in Julian Barnes's The Sense of an Ending. And Vaughan's recovery of his pedagogical passion via a student called Tanika feels sketched more than developed.

But the pluses outpace the minuses by miles. Vaughan's daughter, Dillie, is a glorious creation, whose scatter-shot delivery is beautifully rendered: "-and-what-should-I-get-Grandma-for-her-birthday-oh-it's-How-I-Met-Your-Mother-tonight-can-we-watch-that?"

The show, however, is stolen by Maddy, whose youthful vivacity is captured in flashback: the passage in which she commandeers the public address on an intercity train is a highlight of the book. More rounded than O'Farrell's previous female leads, Maddy elevates this tale of laughter and forgetting into one of understanding and forgiveness.

The moral? Pay close attention – to who you are, who you were and who you are with. Retain your sense of humour. And never leave home without identification.