Felonious Fiction : CRIMINALS,<i> By Margot Livesey (Alfred A. Knopf: $23; 271 pp.)</i>

Following a romantic breakup, Mollie Munro, alone in her dank heap of a Scottish farmhouse, is unraveling fast, hearing voices and imagining black birds divebombing her car. To the rescue comes her stodgy brother Ewan, a London stockbroker with a sense of duty despite troubles of his own. In order to reach Mollie, though, because he doesn’t drive and she’s all but grounded, he’s forced to take a bus from the airport to the town nearest her farm. During a pit stop, he ducks into the station Gents, and there, on the mucky floor, is an abandoned baby.

On such chance occurrences hang the plots of novels--and of lives, according to Scottish writer Margot Livesey’s funny, suspenseful and sometimes creepy new book, “Criminals.” Ewan’s plans for guiding Mollie back to earth are changed forever by baby “Olivia,” whom Mollie names, tends and schemes obsessively to keep. Olivia appears to Mollie as her salvation, a gift that Ewan, she thinks, has “attracted . . . out of the universe not for himself but for her.” She invents obstacles to contacting the police--the late hour, the weather, fatigue--and Ewan, relieved at her high spirits, goes along. Preoccupied with his own role in an insider-trading scandal, he even lets Mollie talk him into going home, with a promise that she’ll return the child herself.

Of course she doesn’t, and Olivia turns out to have a mother who wants her back, even as the mother’s boyfriend, Kenneth--the one who ditched the child in the first place--plots to extort cash from the rich folks who “stole” her. Then Mollie’s boyfriend, Chae, a novelist who betrayed her by caricaturing her feelings in print, shows up full of remorse, wanting her back. Meanwhile, Vanessa, the fellow broker who profited from Ewan’s indiscreet stock tip, surfaces too, to seduce him into lying to the Serious Fraud Office.

Amid all this morally questionable activity, Livesey poses the question: When does an act turn criminal? Where’s the line between an actual lie and the stories kids tell with their fingers crossed to get what they want? “Bad laws are meant to be broken,” Mollie says. But who decides which are bad? Kenneth, the moronic lout who tries to profit from a lost child?

Kenneth, swaggering, brutish, adrift from the human race, is the novel’s most chilling character. He’s also pitiful in his longing for respect--from fellow pub crawlers, his browbeaten girlfriend and his mum, who curtly tells him who he is: “You gormless wonder!” He is gormless--and soulless, incapable of fathoming the pain he causes.

By contrast, some of Livesey’s other characters commit wrongs in order to connect and to be forgiven. Even Chae’s book, so hurtful to Mollie, which Livesey excerpts throughout “Criminals,” seems a twisted plea for attention from the very person whose emotional needs he has denied.

In the same way, the workaholic bachelor Ewan’s moral slip flows from his own repressed desire for love--a slip that leads him so far from himself that he seeks absolution from a Mr. Coyle of the Serious Fraud Office. Coyle’s advice brings us back to Livesey’s setup--to the often absurd collision of chance and free will wherein stories begin.

How, Ewan asks in effect, could he have better navigated the moral thicket that sprang up around his crazy sister, a bus-stop baby and a thug in a bad suit?

“If I were you,” Coyle says, “I’d learn to drive.”