By Nuala O'Faolain

Riverhead. 307 pp. $24.95

In this biography of Chicago May Duignan, crook, prostitute and con artist of the late 19th and 20th centuries, Nuala O'Faolain -- who has written two memoirs as well as a novel -- fills in what sketchy facts she has with her (extremely lively) imagination. She and May both came from impoverished rural Ireland (albeit decades apart); both endured the often-taxing discipline of the Irish Catholic Church; both escaped the burdens of motherhood; both rejected out of hand the pre-planned destiny of all too many Irish women. Both, in their own ways, made names for themselves.

But they aren't all that much alike. The author's imagination fails her at the most critical juncture. O'Faolain is a law-abiding citizen -- a writer, with all the anxiety and wish to please that any writer is afflicted with. Her subject, Chicago May, took her name from a few eventful years in that city, after she spent time in Nebraska and before she went to Egypt and then -- for much longer -- to New York and Paris. ("Crooks, in those days," O'Faolain reminds us, "were named not after where they really came from but after where, in vast, hardly knowable America, they seemed to come from. They had names like Bitter Creek Newcomb, Texas Jack, Klondyke Flo. . . . She never lived in Chicago again and scarcely even visited it, but it was perfectly appropriate that she was known for the rest of her life as Chicago May.") May is by self-definition an outlaw through and through, and a pathological liar besides. Thus, her autobiography, "Chicago May, Her Story: A Human Document by the Queen of Crooks," lies even in its title. She's not the queen of anything. Again, the author must rely for "facts" on this document, filling in the interstices with what she can dream up (the word "imagine" occurs at least 18 times in 307 pages), with a few letters and jail records to tape the whole thing together.

But this can be seen as a logical continuation of O'Faolain's career. When she worked in Irish television, she writes in her prologue, "I made a series called Plain Tales, in which older women looked into the camera and told their life stories uninterrupted, the editing cuts covered by their own innocent snapshots, little pictures faded to sepia of fat babies and girls in old-fashioned coats swinging arm in arm along out-of-focus streets." She wants to give a voice to the voiceless, those "millions and millions of women stuffed and crammed into graveyards who might as well never have been born for all anyone knows about them." By writing a biography of Chicago May -- if I read correctly -- the author intends not only to pay tribute to her but to all Irish women who "fell" instead of living a life of respectability -- particularly the generations of hapless immigrants who sailed to American shores to die lonely and loveless, in brothels or worse.

The author also intends this, she writes, as a tribute to her own luckless brother Dermot, one of her eight siblings. He was pushed heartlessly out of their parents' house to fend for himself, just couldn't do it, ended up an alcoholic and died young. This is a lot of baggage for one book. The project requires passion (which the author has in abundance), scholarship (which the author does her best at), and a good dose of skepticism (which, alas, she seems to lack). She takes Chicago May at her own, literal word. Never mind that a con woman is professionally trained to lie, that by the time she wrote her memoir, in old age, May was caught up in dreams of grandeur, that she was working with a ghost writer, striving to give the thriller-craving public what she must have thought it wanted. O'Faolain buys it hook, line and sinker.

That makes it hard for a reader who can't buy it. May, for instance, runs away from home at 19, taking her family's life savings, "the equivalent of more than five thousand dollars in today's money," O'Faolain writes. But how did a dirt-poor family with no visible means of support, living in a humble four-room dwelling out at the edge of a lonely bog, with at least four children to support, manage to save the equivalent of $5,000 and keep it around the house?

Indeed, there's a crashing dissonance between the quoted May's brio, braggadocio, and belligerence and the caressing way the author treats her subject here. May's tales are all of stealing, conning, punching -- and it's she who's doing the punching, tracking down unfaithful lovers and giving them yet another sock in the jaw. (Of course, she's working with a ghost writer and selling her life of crime to what she hopes will be a credulous public.) O'Faolain, on the other hand, goes for pathos and heartbreak. If she wants to take the writings of an old con woman as gospel truth, that's one thing. But no sooner does the author establish Chicago May as a rollicking, successful outlaw than she begins to tell us of the dreadful conditions of the freezing girls of the street who didn't set their feet on the ground for weeks at a time. But that wasn't May, was it? The author imagines May working in a brothel: When these women were together, "was the presence of others community? No. Each woman must have been chilled in her very being by loneliness." Which is it, then? Was May the swaggering success she portrayed herself as in her own pages or the pitiful victim the author imagines?

When May is jailed for 15 years (one of her boyfriends shot another of her boyfriends and she was involved), the author writes, "I can only salute her experience and step back, when I think of the whole of her life being reduced to one small, stone cell, for every hour of the year and for year after year." Then O'Faolain thinks of the Jewish Museum in Berlin in order to imagine "the terror of the fragile self in incarceration." Wait: The massacred Jews were innocent, whereas May -- after a life of professional crime -- had been mixed up in a shooting. Kind of like the difference between making a thousand in one night and huddling half-naked and penniless on freezing Chicago streets, which the author imagined by standing in that city "where the half-frozen river slid under shards of ice into the lake, dank fog rising as the winter afternoon darkened." The author slanders Ocean Beach, Calif., a blameless little town where my own husband grew up: It was a "bad omen" when Chicago May went there, because, writes O'Faolain, she herself had coincidentally gone there "when I was in my thirties and my life had lost all joy." She bitterly laments "the Irishwoman's fate of domestic service," as if Canadian, Chinese, Russian, Mexican or Sudanese women never have had to wash a dish or sweep a floor. It's more than exasperating -- these fuzzy thoughts, this circuitous reasoning, this compendium of infernal, inaccurate, biographical imagining!

This Sunday in Book World

* Salman Rushdie's "dazzling" new novel.

* Zadie Smith's masterly "On Beauty."

* Julia Alvarez on writing in a post-9/11 world.

* Peter Bergen on the words behind al Qaeda.

* James Webb on The Washington Post's Anthony Shadid.