Ok, here it is, straight from Wikipedia [since they explain it better than I would on such short notice, years since I read the book and seen the subsequent movie]
Once Were Warriors is New Zealand author Alan Duff's bestselling first novel, published in 1990. It tells the story of an urban Māori family, the Hekes, and portrays the reality of domestic violence. It was the basis of a 1994 film, directed by Lee Tamahori and starring Rena Owen and Temuera Morrison. The novel was followed by two sequels, "What Becomes of the Broken Hearted?" and "Jake's Long Shadow".
Beth Heke left her small town and, despite her parents' disapproval, married Jake "the Muss" Heke. After 18 years, they live in a slum and have six children. Their interpretations of life and being Māori are tested. Since Beth is from a more traditional background, she relates to the old ways, while Jake is an interpretation of what some Māori have become. Beth sometimes tries to reform herself and her family - for example, by giving up drinking and saving the money which she would have spent on alcohol. However, she finds it easy to lapse back into a pattern of drinking and irresponsibility. The family are also shown disconnected from Western culture and ways of learning. Beth reflects that neither she nor anyone else she knows has any books in their home, and her daughter, Grace, is the only character with a real interest in school and learning.
Jake is unemployed and spends most of the day getting drunk at the local pub with his friends. There he is in his element, buying drinks, singing songs and savagely beating any other patron whom he considers to have stepped out of line (hence his nickname of 'The Muss'). He often invites huge crowds of friends back to his home for wild parties. While Jake portrays himself as an easygoing man out for a good time, he has a vicious temper when drinking. This is highlighted when his wife dares to 'get lippy' at one of his parties and he savagely attacks her in front of their friends.
***, the Hekes' eldest son, moves out to join a street gang. He cares about his siblings, but despises his father for his thoughtless brutality, a feeling returned by the elder Heke. *** attempts to find a substitute family in the form of the gang, but this is unsuccessful as the gang members are either too brutal or, in the case of ***'s gang girlfriend, too beaten down to provide him with the love and support he craves.
The second son, Mark 'Boogie' Heke, has a history of minor criminal offences, and is taken from his family and placed in a borstal. Despite his initial anger Mark finds a new niche for himself, as the borstal manager instructs him in his Māori heritage.
Grace, the Hekes' 13-year-old daughter, loves writing stories as an escape from the brutality of her life. She also spends time spying on a wealthy Pakeha family who live nearby. She is amazed at the contrast between their lives and hers - not simply the material wealth, but also the lack of conflict in their lives. Grace's best friend is a drug-addicted boy named Toot who has been cast out by his parents and lives in a wrecked car. He is the one who really cares for her.
Grace is raped in her bed one night, and she subsequently hangs herself. In her diary, later found by her family, Grace says she thinks it was her father who raped her; Jake, who had been too drunk to remember what happened that night, has no answer. He leaves his family and starts living in a park, where he reflects on his life and befriends a young homeless man. Meanwhile, Beth starts a Māori culture group and generally attempts to revive the community.