Inez Isabel Maud Peacocke was born in Devonport, Auckland, on 31 January 1881. She was the daughter of Emily Frances Mitchell and her husband, Gerald Loftus Torin Peacocke, a Madeira-born English barrister, later editor of the New Zealand Farmer. Isabel's carefree childhood was spent by Cheltenham Beach, near Devonport. She was educated privately and then, in her early 20s, spent a year in England and Europe.
When she returned to Auckland the Dilworth Ulster Institute, later the Dilworth School, had been established for disadvantaged boys. In 1906 Peacocke was appointed as the first, and initially sole, teacher; by the end of the year there was a roll of 15 children aged from 6 to 10. She quickly established a reputation as a storyteller; some of her tales, as well as her retellings of the classics, were later published in Whitcombe's Story Books series.
Peacocke published her first children's novel, My friend Phil, in 1915, and was to publish 25 in total. Her experiences at the school undoubtedly contributed to her acute and often humorous observations of children, but they did not tempt her to write stories about school life, which were the most popular genre of the period. Her interest lay less in the interaction between children than in the relationship between parent and child. Many of her parents are at best snobbish, at worst irresponsible. The wise and good-humoured adults in her books are kindly uncles and aunts who take over where mothers and fathers have failed, and central to a number of stories is the problem of guardianship.
No other New Zealand author has given a more detailed picture of the period of the First World War. Soldiers leave for, and sometimes return injured from, the battlefield. Children are fatherless, unemployment and tuberculosis take their toll and people die because they cannot afford a doctor. In the 1920s Peacocke turned her attention to snobbery. In both Quicksilver (1922) and Marjolaine (1935), children of differing social backgrounds face obstacles to friendship from the wealthy parents of one or other of them.
On 30 June 1920 in the Holy Trinity Parish Church of Devonport, Peacocke married George Edward Cluett, a 66-year-old engineer from Portsmouth, England. They lived in Remuera and the next 16 years of a very happy, but childless, marriage saw some of her best children's writing. George Cluett died from cancer in 1936, and thereafter Peacocke wrote almost exclusively for adults under her married name.
These 16 adult novels lack the humour and vitality of her best work for children and are often overtly didactic. All of them show a reverence for marriage, which she sees as offering protection for women. The earlier books take for their themes the threat to young women's virginity from predatory males. In the later stories marriages themselves are threatened, and resolution of the difficulties is seen as preferable to divorce.
Peacocke's novels, both for children and adults, are a celebration of Auckland and its environs. Her characters sail on the harbour, take trams along Karangahape Road, and sometimes catch a rickety bus which rattles over dirt roads to the bush of the Waitakere Ranges and the magnificent surf beaches of the West Coast. Cheltenham Beach, where she grew up, is the setting for two of her children's novels and for the autobiographical When I was seven (1927). In spite of this sense of place she was little known in New Zealand. All her novels were published in Britain and distribution arrangements were poor.
Peacocke became increasingly involved with the literary scene in Auckland. She was a frequent contributor to the New Zealand Herald, a founding member of the New Zealand League of Penwomen (president in 1930), and a member of the Authors', Artists' and Playwrights' Association in London. A popular broadcaster, especially on the subject of Auckland, she delved into local history, presenting it in a lively, accessible manner. However, Peacocke never abandoned her interest in young people. She was a long-term supporter of the YMCA and of the Childhaven Association.
Peacocke's final years were spent in the Roskill Masonic Village, Onehunga, where she died from heart failure on 12 October 1973. She was buried with her husband in the Purewa cemetery. She had suffered the misfortune of living long enough to see her writing become unfashionable. Her greatest literary fault was undoubtedly an unevenness of style. Although at best her prose was incisive and satirical, at worst it was self-consciously slangy and coyly sentimental. She was, nevertheless, an accomplished storyteller, who knew the art of keeping the reader engrossed, and no other New Zealand writer has so convincingly depicted the life and times of Auckland in the years between the wars.