"Please don't feel you always have to be good," eight-year-old Barnaby Johnson is advised on what is almost the final page of Patrick Gale's new novel. "Sometimes you're so good it hurts to watch you."

Wise words, but in the book  which spans the Cornish parish priest's life from youth to late middle age  they go largely unheeded. It's a famously tough task, attempting to mine the life of a "good" man for suspense, ambiguity and drama. Fortunately, Gale's dog-collared protagonist is far more complex  and sinful  than we originally suspect. And, far from being a dull cipher, he is also that rare thing  a fictional character so charismatically ambiguous, so physically, spiritually and emotionally alive, that you feel you could reach out and ruffle his hair. Forget what they say about the Devil. There's a pretty good tune being tapped out here in these Anglican pages.

The novel opens with a parishioner's suicide: 20-year-old Lenny, paralysed in a rugby accident and about to spend the rest of his life in a wheelchair, asks the priest to visit, only to swallow poison in front of him. Shocked, Barnaby prays for him  then offers himself up for arrest. It's a credit to Gale's sly yet wholly plausible plotting that I neither guessed, nor ever doubted, the events and revelations which follow.

But then this is a novel whose primary suspense lies not in the "what", but the "when" and "how". Our glimpse of the eight-year-old Barnaby is actually the last in a series of snapshots which dip in and out of his life and that of his family. They seem to come in no particular order, but in fact very deliberately and effectively build a compelling narrative. So we have "Barnaby at 52" or his wife "Dorothy at 34" or parishioner "Modest Carlsson at 39". Gale's skill is to keep perspectives constantly shifting and to keep us wondering quite how all these separate destinies will collide.

The collision we await with most interest (and trepidation) is the one between Barnaby and Modest. The parishioner is a former teacher who had to relocate and change his identity following a liaison with an under-age pupil, which cost him his job, his marriage and, possibly, his soul.

In Modest, Gale gives us an all too chillingly credible definition of everyday evil  a self-loathing oddball who likes to spend "long afternoons in bed with a bag of cheap chocolates" and who recognises Barnaby as prey to be chased and, in some way, consumed. Craving encounters with the priest, and of course benefiting from the innocently inclusive nature of the Christian community, Modest tracks him in ways which feel increasingly disturbing and dangerous.

This man is a vividly queasy creation, a character who seems somehow to exist on the very edges of Gale's writerly comfort zone. I was never quite sure what the novelist was going to do with him, how far he was going to push this darkness, how worried I ought to be. Maybe that's because one of Gale's biggest strengths is his narrative compassion  he understands how it feels to be anyone, man, woman, child, young or old. Even the animals in this novel affectionately illuminate their human counterparts, and it's no surprise to learn of Modest that "Dogs and cats, any pet, disgusted him".

Not only that but Gale is especially acute when it comes to the shifting dynamic of marriage, and noticeably astute and unsparing about parenting, the easy joy, the helplessness, the weary despair. In a scene that continued to bother me long after I'd read it, Barnaby and Dot's adopted son, supposedly in rehab but in fact whacked-out on amphetamines, graffitis "Fuck Jesus" on the church in red gloss. His parents assuage their shock and grief by calmly painting it over with whitewash, listening to a Prom on the radio, eating fish and chips and enjoying a moonlit walk while the emulsion dries. Later they surprise themselves by making love for the first time in 15 years. It is a deceptively tender yet appropriately troubling episode which seems to cut to the marrow of what it is to be a parent.

At his best, Gale is an effortlessly elastic storyteller, a writer with heart, soul, and a dark and naughty wit, one whose company you relish and trust. In fact you feel you would believe anything he told you  and if I have a small complaint, it's that he sometimes doesn't quite seem to realise it, doesn't trust in his own genuine power. Now and then he writes a little too hard, too carefully or too deliberately. Relax, you want to tell him. Trust yourself, because we do. Do less, because what you do is already so effective. But it's a minor quibble in a novel which managed to upset and uplift me in equal measure, and which kept me company  and kept me guessing  right through to its slightly bitter and heartfelt end.

Julie Myerson's most recent novel is Then (Bloomsbury)

The gentle irony implicit in the title of Patrick Gale's latest novel sets the tone for the whole book. The familiar phrase exemplifies a peculiarly English irony, implying a quality of goodness that falls far short of perfection and yet, at the same time, is acceptably sufficient. It has overtones of the great child psychologist DW Winnicott's famous "good-enough mother"  that is, a mother who fulfils, by and large, the basic needs of her child.

The "perfectly good man" in question is Barnaby Thomas, the priest of a rural parish in Gale's native Cornwall (the Cornish countryside and weather is rendered with reassuring authenticity). We follow his life, spiritual and psychological, from his own perspective but also from that of the various characters who are germane to that life: his wife, Dorothy, who against her own preferences is tellingly morphed by her husband into "Dot"; his daughter, Carrie; his adopted Vietnamese son "Jim", who, in the course of the book, elects to return to his native name "Phuc"; and a very creepy parishioner who goes by the name of "Modest Carlsson". In fact, the novel has quite a bit to say about the process of shifting identities; this parishioner's name has also been subjected to a change, to conceal a former prison sentence for paedophilia.

The novel opens, startlingly, with yet another character, the 20-year-old Lenny. Lenny has been paralysed by a rugby accident and is condemned to a life in a wheelchair. As a result, he has broken off his engagement to a devoted childhood sweetheart and, when we meet him, is preparing to take his life. Barnaby, who supposes he has been summoned for no more than spiritual counselling for a beleaguered parishioner, finds himself, perforce, a witness to the deed. Before calling for help, he spontaneously administers the last rites and then, with a characteristic lack of self-preservation, as a party to the young man's suicide, surrenders himself into police custody.

The full significance of Lenny's relationship to his parish priest is not revealed until much later in the novel, which is structured in such a way that we not only jump from one character's consciousness to another but also move within those individuals' histories, back and forth in time. This is a bold and highly effective technique. The non-linear disclosure of character and motive places the reader somewhat in the position of the psychoanalyst  witnessing at one moment the middle-aged vicar struggling with a withering faith and later, at the end of the book, that faith's foundational moment in childhood.

The same technique brings us close to Dot: the domestic tragedy of her child-bearing failures, its consequences for the intimacy of her marriage and the concomitant decision to adopt a Vietnamese orphan. Gale sensitively unravels the ripple effects of this apparently worthy decision, on Dot but also on the boy himself and his lumpen but loyal sister. Enmeshed with all this is our developing understanding of the vile Modest Carlsson, whose sinister fascination with Barnaby is an unrecognised catalyst both of Lenny's birth and Dot's untimely death.

What Gale does so well is to delineate the unpremeditated spider-web consequences of actions, most particularly those where the intentions are apparently perfectly "good". The unfolding nightmare for all the family of the consequences of adopting are exquisitely and painfully documented. Phuc, returning to his native identity, turns on his adoptive parents and country, and escapes into alcoholism and drug abuse. This could be clichéd, but is saved by Phuc's utterly convincing retreat into a saving relationship with a much older woman, whose children he helps and befriends. None the less, he remains unable to restore a loving relationship with his adoptive father who, again convincingly, cares more passionately for his adopted son than for his flesh-and-blood daughter.

The strength of this novel lies in its capacity to convey ordinariness authentically: ordinary love, ordinary failure, ordinary belief, ordinary, everyday tragedy, which of course in its particular manifestation is never "ordinary". Gale is a writer whose very facility makes him an easy read. This can mean that his subtle moral and psychological insights can be overlooked, which is a pity, as most of us  for better or worse  lead just such ordinary lives. He is also skilled at creating intimacy between a character and the reader. By the end of the novel, we feel we really know Barnaby, warts and all, and his wife and children, and our sympathies for them are not unlike our sympathies for ourselves leading our own imperfect lives. This is not to imply that Gale cannot also hint at the sublime. The final chapter left me with a lump in my throat because it so beautifully captures the shining, vulnerable promise of childhood.

 Salley Vickers's The Cleaner of Chartres will be published by Viking this autumn.