With bizarre symmetry, Diana Petre performs for her mother somewhat the same service her half-brother J.R. (Joe) Ackerley performed for their father. Joe's My Father and Myself (1969), a sexual autobiography of outrageous sang-froid and bravura, took as its starting point a chimerical quest for shared sexual identity with the elusive Alfred Roger Ackerley, a prosperous fruit merchant of the staidest propriety who got around to marrying Joe's mother only when their three children were grown. His death in 1929 revealed the existence of ""the secret orchard"": another non-wife with three children. Muriel Perry was working at a fashionable bar when Roger, 27 years her senior, became her lover, father, protector. Whatever her life before that, she concealed it with such near-psychotic intensity that to this day Diana has not been able to identify so much as the names of Muriel's parents. The mother Diana knew was disturbed to the point of inaccessibility: a confused, unprepared parent, a lonely woman (""Uncle's"" contribution was chiefly financial), an appalling alcoholic. Incurably depressive, she came fully alive only in times of epic crisis. She served heroically in WW I and was a prisoner of the Germans in the second; when there was no war on, her life tended toward maximum entropy. When the twins were two and Diana an infant Muriel disappeared, leaving them to the care of a housekeeper. She showed up with the most perfunctory explanations ten years later and embarked on a nightmare parody of motherhood that drove all three girls to despair and eventually flight. Try as they would, they could never eradicate the lonely, self-deluded woman from their inner (and outer) lives. Comparison with My Father and Myself is inevitable if unfair; it is the comparison of a wonderfully well-written book with a crabbed masterpiece. Petre's approach is deliberately more geared to conventional biographical expectations than Ackerley's; her prose style, acridly penetrating and handsomely honed though it is, aims for smaller effects; she puts together her story with less extravagant ingenuity. Despite the long shadow of Joe, this remains a flawless achievement in its own right.