READERS OF THE first two volumes of New Zealand writer Janet Frame's autobiography, To the Is- land (1982) and Angel at my Table (1984), will recall her early life as horrific. As a child, she experienced poverty, neglect, family illness and a sister's accidental drowning. In her twenties she was, by her own account, misdiagnosed as a schizophrenic and spent eight years in and out of New Zealand mental hospitals, where she was subjected to electric shock therapy and narrowly escaped a lobotomy. A second sister drowned. By this time she was, if not insane, almost neurotically insecure, passive and shy, barely able to function in public. Evidently, the sole sustaining force in Janet Frame's life was her belief in herself as a writer. Literature, as she says in To the Is-land, was her "real" life.

Faithful readers will therefore find The Envoy from Mirror City a wonderfully satisfying book. It describes how the ugly duckling, the victim of appalling mistreatment in her own country, was resoundingly vindicated abroad, and it gives us more of that same fine prose, at once lucid and concrete, always suggesting obscurer depths beneath the clear surface, which distinguished the earlier volumes at their best.

Perhaps Janet Frame's most notable achievement in these memoirs is the way she can use this understated, apparently artless style to convey simultaneously her naivet,e and awkwardness as a young woman and the powerful, ironic intelligence she too often concealed. Schizophrenic or not, she did lead something of a double life. Publicly, she was apt to feel "the sudden unfriendly chill of being just myself and no-one else: not dainty but with legs that my sister had said were like a footballer's legs." Only inwardly was she fully herself. "I retreated again into my own habitat, looking out at all worlds," is how she describes the ending of one unsatisfactory relationship, her "own habitat" being nothing less than "Mirror City," the iridescent private world of her imagination.

THIS BOOK OPENS with Janet Frame sailing off to Europe in 1956 with a literary grant, to "write," though her first two books had already been published in New Zealand. She was a thoroughly unconventional traveler, despite her utterly conventional appearance, and hers proves to be a memorable odyssey. After a brief sojourn in London, she set off for Ibiza, in the Balearic Islands of the Mediterranean, where she had been advised one might live "for three or four pounds a month": an artist's paradise. With that combination of passivity and daring which seems to have stamped her personality, she found a place to stay in Ibiza by the simple means of approaching two black- shawled women gathering twigs and branches by a road. "I spoke hesitatingly. 'Jo soy de Nueva Zelanda. Janet. Quiero habitacion.' I placed the palms of my hand together and rested them against my cheek."

The place "Catalina" and "Francesca" took her to became home for "Janetta" for the next few months. She tried the same approach later in Andorra, having fled Ibiza and a failed love-affair, and this time barely escaped an arranged marriage with an illiterate Italian smuggler. "And so it happened again that . . . I found myself assuming my most accustomed role, that of the passive person whose life is being planned for her while she dare not, for fear of punishment or provocation, refuse."

Back in London, she spent months in and out of the Maudsley Hospital Institute of Psychiatry, where she was finally given back the double-edged gift of herself, freed of the old, false stigma. "I had never suffered from schizophrenia. . . . I should never have been admitted to a mental hospital. Any problems I now experienced were mostly a direct result of my stay in hospital." Having learned, slowly and painfully, to accept the responsibility for her own life which went with this newfound freedom, Janet Frame was spectacularly enabled to write again: her brilliant, original novels Faces in the Water, The Edge of the Alphabet and Scented Gardens for the Blind, as well as two volumes of stories, were all written and published during her four or five remaining years in London. Today, Janet Frame is probably New Zealand's most honored living writer.

That is why the metaphor of the "Mirror City," which gives this volume its title, is so important in the book: it represents the attempt of one of the major fiction-writers of our time to explain her own creative processes. The image dates back to Janet Frame's days in Ibiza, where her bedroom had "a wide window overlooking the harbour and the distant shore where the buildings lay like those of another city, a sea or mirror city reflected in the clear water." Although she has difficulty explaining something which she herself obviously experienced as a kind of epiphany, a charged symbol rather than an intellectual concept, Janet Frame clearly identifies her "mirror city" with the creative imagination, reflecting back the real world transformed. And "the self must be the container of the treasures of Mirror City, the Envoy as it were, and when the time comes to arrange and list those treasures for shaping into words, the self must be the worker, the bearer of the burden, the chooser, placer and polisher."

Some readers will value the book for these and other literary insights; others will appreciate more easily Janet Frame's comic spirit, her courage and honesty. For all these things, the entire trilogy is a work to treasure.