EVELYN WILDE MAYERSON has rapidly staked out her own corner in a particular literary territory. She writes about people from whom we might generally avert our gaze, and she writes about them sympathetically but without the slightest sentimentalization. Sanjo, her first novel, had for its heroine a 34-year-old victim of Down's syndrome. This second novel describes the life of a bag lady -- the middle-aged, schizophrenic, and not-so-sweet-smelling Hester, a vagrant in the streets of Philadelphia.

Stationed on a block of peep shows and "martial aids" shops, surrounded by a cast of numbers runners, juvenile delinquents, prostitutes and flim-flam men, Hester ekes out an existence so perilous that she compares it to "crossing a frozen river that is beginning to thaw, jumping from one piece of ice to another, never knowing when the ice floe upon which you stand will begin to break up again." She prefers that, though, to confinement, and this is what propels the story along -- her struggle against the do-gooders who want to rescue her. To Hester, freedom is everything -- as it is to the escaped falcon soaring overhead (a symbol hammered in just a little too hard and too often, I thought).

We first see Hester uncoiling from a night's sleep in a doorway, looking like one of her own shabby bundles, and -- as with Sanjo -- we wonder if this is really someone we want to know. But Hester has her winning ways. She's refreshingly nonchalant about her life ("Pointy end down!" she warns a child thief who is running away with her scissors) and often very funny. ("You can't be chaste when you're married," she tells a friend. "They get after you in the night and spoil a whole day's work.") There is a salty quality to her that keeps surprising us. Wait, we think, this lady's sharper than we gave her credit for.

But she's also genuinely, certifiably insane, and it's in describing this state that Evelyn Wilde Mayerson is most convincing. Hester seems to see through a kind of fog that now lifts, now descends. She expects no logic from life, and merely tries to brace herself for the next inexplicable situation it may have to offer. When a doctor treating her for frostbite asks, "Do you know why we need to amputate your feet?" her answer is prompt: "You have a quota." (How much that single sentence reveals of her view of the world!) When a policeman arranging for a marathon announces that 2,000 people will soon be running through the streets, Hester asks, "Is it the dam?" She has an invisible friend named Dunce; she believes she must shake her heart into place every morning so the attachments to her brain will hang straight; and she is startled now and then by wisps of troubling memories which -- with the lightest of touches -- tell us exactly as much as we need to know about her crippling past.

She is often ridiculous, disoriented, or given to inappropriate reactions. Visiting a friend in the hospital, for instance, she grows bland and expressionless when she sees that he's dying. "I found a new recipe for you when I was changing papers," she tells him, and she pulls some of the newspaper padding from inside her stockings. "It tells you how to cook an artichoke."

As an exploration of a single character, then, this book is fully as successful as Sanjo. But once you step back from Hester and examine the novel as a whole -- its method and tone -- If Birds Are Free seems more artificial than its predecessor. It often appears told from outside, by a lofty, anonymous observer gazing down upon the hapless Hester. When Hester speaks to someone who's not there, we're told that "Hester was hallucinating. The confusion was in her chemistry, a metabolite gone sour that made her hear a voice." Just when we're settled into Hester's skin, or some other street character's, we are jarred by information that neither Hester nor her friends could possibly possess: the exact, scientific names for the tubes inserted in a hospital patient; the history of a certain policeman's career; the criminal record of a department store Santa; a sophisticated explanation of the guilt that compels a blind beggar's patrons; even the fact that the croutons thrown to some pigeons are garlic flavored.

It's not that I'm against omniscient narrators, but there's a constant shifting here that's downright head splitting. We've barely started to enjoy a comical psychiatric interview, with Hester thinking to herself how silly the questions are, when we're told that the psychiatrist "was as stumped as he had been for two days when he agonized over 14 Down in the Sunday puzzle, shouting at his girl friend, who knew the answer, not to tell him and warning her that she was beginning to display exactly the same attitude as his estranged wife, which was, he had warned her, entirely counterproductive to a healthy relationship."

Too much cleverness. Too many knowing side glances at the reader. Evelyn Wilde Mayerson has a wonderful touch with life's losers, but I hope that in her next book, she'll stay close to them all the way through and leave her audience to manage on its own.