Today is one of the biggest days in publishing history - a second book by Harper Lee will hit the shelves, 55 years after the publication of the classic To Kill a Mockingbird. Discovered this year, Go Set a Watchman is a strange beast - a sequel to Mockingbird written before it. It is the book that Lee originally submitted to the JB Lippincott publishing company. Her editor, Tay Hohoff, was impressed by the writing but felt the book was not fit for publication and suggested that Lee work a series of flashback sequences told from the childhood perspective of her main character into what became the book she is revered for writing.Now after months of speculation about whether the 89-year-old Lee had been coerced by her publishers into releasing it, Watchman has arrived.Unless you're Michiko Kakutani, the books editor of The New York Times who makes and breaks literary careers like some women buy shoes, you're unlikely to have had the chance to read more than the first chapter released by The Guardian in the UK over the weekend and accompanied by a 16-page supplement.Watchman follows grown-up Scout from Mockingbird as she makes a journey home in the post-World War 2, nuclear age to visit her ageing, arthritic father, Atticus Finch, the liberal beacon for a generation of human rights lawyers who fought against the racism of the town of Maycomb, Alabama, and stood up for justice in the rape case at the centre of Mockingbird.In his old age, Atticus has become a shadow of his liberal younger self. Now he's a bigot spouting hate speech about negroes and attending meetings of the KKK. This is the single greatest revelation of all the hype around the book and for many fans it may rankle to accept Atticus (based on Lee's own lawyer father) as having become everything that he fought against.However, as Mark Lawson, reviewing the book in The Guardian, says, although some fans of the earlier novel might find it "like discovering an alternative version of The Catcher in the Rye in which JD Salinger casts the story of the adolescent Holden Caulfield as the dream of a paedophile Republican senator", the writing stands up and the book is "a new work, and a pleasure, revelation and genuine literary event, akin to the discovery of extra sections from TS Eliot's The Waste Land or a missing act from Hamlet hinting that the prince may have killed his father".It seems the great tragedy of Go Set A Watchman is not that it is not To Kill A Mockingbird but rather that it is only the second piece of writing ever published by Lee.Go Set a Watchman, published by Cornerstone, R330..