Perfect stranger

The Accidental
By Ali Smith
Pantheon, 305 pp., $22.95

''The Accidental" is a thoroughly charming and melodic novel, but you shouldn't let either of those qualities get in the way of its fierceness or its metaphysical precision. As with the Scottish author's ''Hotel World," published here in 2001, the story exudes a certain eerie caprice: mystery characters and revelatory connections, wordplays and delights in language that belie its somber themes. Ali Smith will write an allusive, near-rhapsodic passage about the history of cinema, then do cartwheels with the sonnet form and make jokes about Philip Larkin. Underneath the dazzle and the high-wire fun is a novel that belongs not to literary shenanigans but to old-fashioned trouble and redemption.

The book's premise is an ancient theme: A stranger appears at the door, gains admittance, then proceeds to change your life. The lives that very much need changing here belong to the four members of the Smart family, who are dragging their heels in a disappointing summer rental in Norfolk. ''The Accidental" unfolds in shifting perspectives, and the first belongs to Astrid, a 12-year-old girl who deserves the surname she's begrudgingly inherited from Michael Smart, her stepfather. She's acute and funny and half-bleak with insight, feigning nonchalance but looking for connection, and she roams the rooms and lanes of Norfolk with her new digital cam, filming dark little moments in order to own them. Magnus, her older brother, is on the verge of a breakdown. He was instrumental in a cruel high school prank during spring term, and its disastrous results have sent him spinning into an abyss where he's convinced he belongs.

The parents seem jollier than either Astrid or Magnus, but that's only because they've discovered the adult mechanisms for faking it. Eve Smart is a soprano-pitched gadfly who tries to please everyone; this trait is so nearly pathological that she spends her days writing books that ''imagine" the lives of real dead people, had they managed not to die. The monographs are bestsellers, of course, Lazarus being a constant draw. Her second husband, Michael, cheerfully shoulders his brooding stepchildren and slightly desperate wife, but his good nature is mostly a result of his sleeping around. He's an English professor in London, and half the female students who cross his door wind up with crooked knickers at the end of the session. Eve bears this knowledge with restraint if not dignity, and so the Smarts endure -- each in a form of solitary confinement and each waiting for rescue, whether anyone can admit it or not.

So in walks Amber; like her name, she is dangerously sharp and changes with the light. The woman looks to be about 30 and has a shabby sort of beauty, made more interesting by her insouciance. When Astrid first spots her she is lying on the living room couch -- her old Volvo broke down, it seems, and while unapologetic, she doesn't take up much room, either. Eve assumes Amber is one of Michael's tartlets, Michael thinks she's come to see Eve, and the kids don't much care where she came from, only that she seems capable of marvelous and frightening things. To Astrid, she is both liberator and challenger, taking away the girl's camera and making her look at the world; a rough mother bear and a playmate at once. For poor struggling Magnus, she is a lifesaver in every way that matters. Michael wants to sleep with her and of course cannot, a temptation denied that will be his deliverance. As for Eve, she must face the fact that all her little resurrections have brought her square up against her own emptiness. ''You're an excellent fake," Amber tells her warmly, exposing her every lie and insecurity. ''Very well done. Top of the class. A-plus." Like Cassandra, our visitor prefers the truth.

The more vexing question is how Smith manages to make a simple and fanciful story so transfixing. Whether gypsy tramp or mythic creation, Amber quickly becomes as credible to us as she is to her half-reluctant hosts. For one thing, she's ornery and brash, demanding more of her minions by pushing them around, so no Good Witch Glinda she. Her creator has diffused the fantastic into the real without a hitch, in other words, and that in itself is a kind of magic.

Some of the explanation for Smith's satiny accomplishment lies with the authenticity of the voices. Astrid, ''typical and ironic," as she would say, is slightly fey and completely captivating, particularly when she goes from armor-clad to vulnerable. Magnus is a math whiz who breaks the world into acceptable calculations: The world is getting darker, he knows, as a result of pollution and leached-out sunlight -- the same thing that's happened to his own soul.

While the adult Smarts may be less sympathetic, Smith depicts them with such exacting care that you even feel a bit sorry for old lecherous Michael, particularly when it's clear he's going to get what he has coming. And then there is Eve -- great maternal fount, in search of something beyond her own artificial resuscitations. Id est, says Astrid; the woman needs to jump-start her own life.

''The Accidental" was short-listed last year for England's Man Booker Prize, and was the accidental darling of a lot of critics. It's easy to see why: The novel is small and glistening, one confident little shooting star instead of a cumbersome light show. Its narrative passages in between the Smarts' inner odysseys are devilishly lovely: Smith will do a brilliant riff on the movies, burying lines everywhere from ''Black Beauty" to ''Love Actually," and do it all effortlessly, id est, backward and in high heels. It is not often that such devices are delightful rather than distracting; in ''The Accidental," they are pure confection.

Smith's point with all these acrobatics is one about illusion -- about the truths and lies and special effects that shape us, cure us, point us toward the sea. Because Amber is all things to all her Smarts, she's the perfect imaginary friend -- the corrective experience, in Freudian terms. Watching his kid sister at dinner one night, Magnus considers that ''everybody at this table is in broken pieces which won't go together, pieces which are nothing to do with each other." With Ali Smith and her inimitable Amber at the ready, the broken pieces stand a chance at becoming prisms of light.

Gail Caldwell is chief book critic of the Globe. She can be reached at caldwell@globe.com.