A drunken widow in a gilded cage

In the dedication to Long Day's Journey into Night, Eugene O'Neill describes how his wife Carlotta's love enabled him to "write this play - write it with deep pity and understanding and forgiveness for all the four haunted Tyrones''. The playwright showed less compassion for his descendants: on his deathbed, he "cursed his children and their offspring and the offspring to come.'' It's this curse, in the view of Patrice Chaplin, that her former mother-in-law, Oona O'Neill Chaplin, bore for the rest of her life.

For O'Neill, genius seems to have been less an infinite capacity for taking pains than for evading responsibilities. Oona saw her father only half a dozen times after he abandoned his family when she was three. This did not prevent his sending her censorious letters concerning her frivolity (in 1942 she was Deb of the Year) or protesting bitterly when, in the company of her friends, Carol Marcus (later Saroyan, later still Matthau) and Gloria Vanderbilt, she journeyed to Hollywood. There, she married a man three times her age and even more famous than her father: Charlie Chaplin.

At first, neither Chaplin's staff nor his associates took her seriously and she was not even given control of her own home. She gradually asserted her place until, by the time of her husband's death, she was both a respected matriarch and in control of a large financial empire. Her loyalty to Charlie was unswerving and they remained lovers until he was well into his eighties. But her devotion to her husband led to the alienation of some of her eight children, particularly her favourite, Michael, who married the author of this account.

Patrice was a natural choice to write her mother-in-law's life. They maintained close, if sometimes strained, relations long after she and Michael divorced. Oona admired Patrice's novels and even toyed with the idea of authorising the book herself. After Oona's death, Patrice put the idea to various of the children (despite their age, their behaviour makes the noun particularly apt), but their opposition led her to abandon the idea of a full-scale Life in favour of a personal memoir, focusing on Oona's 14 years of widowhood.

Oona was not a merry widow but a drunken one. After 30 years as the archetypal bird in a gilded cage, she flew off - into a vat of whiskey. This was partly delayed adolescence and partly revenge for a life spent as the perfect wife and mother. On a deeper level, it was a manifestation of the pattern of addiction that had affected her father, her mother, her uncle, her grandparents and her brothers. She also repeated the pattern of her courtship by embarking on spring-autumn romances with Ryan O'Neal and, reputedly, David Bowie. Oona's children were horrified by her behaviour - and their horror apparently returned on seeing it in print.

Patrice, a reformed alcoholic herself, shows more sympathy; but then her attitude to Oona is a mixture of the reverential and the competitive. She seems constantly to compare herself to her erstwhile mother-in-law and to bask in reflected Chaplin glory, referring to them more than once as the Royal Family of show-business - although they often seem more like the ruling family of an Italian Renaissance city state, such as the Borgias.

This is a far from complete life. The lack of detail about Oona's meeting with Charlie, for instance, makes it seem more of a fairy-tale romance than it must have been; nothing is said of Oona's politics and little of her close friendship with Truman Capote. Yet it is the very subjectivity and selectivity of Patrice's account that give it its power.

She writes from a position of informed ignorance, dotting the book with rhetorical questions about motives and relationships. By retracing her steps as a licensed intruder in a very exclusive family, she leads her readers far closer to the enigma of an extraordinary personality than any amount of conventional research.