By Harper Lee

William Heinemann, $45. Buy now on Booktopia

To Kill a Mockingbird was one of the most remarkable literary phenomena of the 20th century, a novel that garnered for its author, Harper Lee, massive sales and universal accolades after its publication in 1960. Lee, now 89 years old, has never published a follow-up work. But this month her first draft of Mockingbird was published under the title Go Set a Watchman, with Lee saying she was "surprised and delighted" when her lawyer recently rediscovered this manuscript.

Despite widespread reservations about the wisdom of its publication, Go Set a Watchman is actually a very worthwhile novel in its own right. The central character is Jean Louise, known in Mockingbird as "Scout", but now aged 26 and living independently in New York. Whereas Mockingbird was set in the 1930s, Watchman is set in the 1950s, and this time difference is crucial.

In an act of editorial brilliance, Mockingbird's original editor, Tay Hohoff, encouraged Lee to reposition the story 20 years earlier, away from the tensions around civil rights that boiled over in the American South after the Supreme Court's decision in 1954 to desegregate schools. Mockingbird's strategic distancing of these racial politics made the book appear less confronting, with its use of a first-person perspective, relating events through the eyes of a six-year-old child, also enhancing a mood of empathy rather than conflict.

But in Watchman two decades have passed, and the plot turns on a trip made by Jean Louise back to Alabama to visit her ageing father. Although written as a first draft of Mockingbird, this book feels in many ways like a sequel. Watchman, told in a more analytical third-person narrative, charts Jean Louise's growing realisation of how her adored father, Atticus, shares the racist sympathies characteristic of his time and place. The court case in Mockingbird, where Atticus heroically defends "Negro" Tom Robinson against a racially motivated charge of rape, is mentioned here only in passing, with Jean Louise now concerned more about her father's opposition to civil rights. This leads to the heroine's self-conscious scrutiny about defining her "own kind," a question brought into focus by the dilemma of whether to marry her old school friend, Henry Clinton, whom Atticus has groomed to take over his legal practice. There are more adult psychological tensions in Watchman, and indeed Henry calls Jean Louise "a Jekyll-and-Hyde character". Looming over everything is a complicated father-daughter relationship, with Jean Louise being told by her uncle that "you confused your father with God".

If Watchman rather than Mockingbird had been published in 1960, it would probably have been recognised as an interesting minor novel in the tradition of Southern Gothic. The spirit of Lee's childhood friend Truman Capote hovers over Watchman's dark style, as well as its Freudian subtexts, and there is also considerable satirical humour in the book's representation of white Alabama. In our own age of Barack Obama and Toni Morrison, Lee's horizons might appear very narrow, and the voice of the African-American community remains tellingly silent here. Atticus' sister Alexandra warns Jean Louise against going to visit their old cook, Calpurnia, since "nobody in Maycomb goes to see Negroes any more, not after what they've been doing to us".

Lee was always concerned about how she could follow Mockingbird's extraordinary success, but it is a tribute to her craft to say Watchman is a worthy successor, even if its direct engagement with the culture of the 1950s makes it a more uncomfortable read than its predecessor. Watchman does not shy away from complexity or ambiguity and it will probably elevate Lee's reputation among literary scholars, even if many of Lee's diehard fans may  –  like the book's heroine – be dismayed to find the characters they once idolised turn out to have feet of clay.

Paul Giles is Challis Professor of English at the University of Sydney.