The Day After Tomorrow by Allan Folsom Little Brown $171 PUBLISHERS Little Brown paid the highest advance yet for a first novel to Allan Folsom for this book - US$2 million (HK$15.5 million). The film rights have been optioned to MGM producer Richard Zanuck for US$750,000 and there seems little doubt it will be made. Zanuck is considering Harrison Ford, Tom Cruise, Gene Hackman and Clint Eastwood for the leads and Folsom sits ensconced in his new Santa Barbara home working on the screenplay, for which he has been paid another US$750,000. Philippa Harrison, managing director of Little Brown, describes the book as a landmark, a once-in-a-decade novel. Folsom himself, when he heard that Harrison had decided to stump up US$2 million for it, was incredulous. ''It's only a book,'' he later told a reporter from Publishing News. Folsom is closer to the truth than Harrison. The Day After Tomorrow has all the right devices, all the right tricks of the thriller writer's trade - the breathlessly short chapters, the subtle recaps for those who may have missed the important points - but it is only a book. Harrison's claim that it will ''dramatically alter the course of the genre'' is hopeful. The inspiration for the opening scene came from a holiday Folsom and his wife took in Paris. Paul Osborn, an American orthopaedic surgeon (Harrison Ford or Tom Cruise?) looks up from a glass of wine in a bar to see the scar-faced man who, years earlier, had stabbed his father to death in the street. Meanwhile, legendary Los Angeles police detective Paddy McVey (Clint Eastwood or Gene Hackman?) has seven headless bodies and one carefully severed head on his hands, but no suspect. McVey's investigation takes him to London, then Paris, where he implicates Osborn and causes amusement among the French police. ''Where most of the world carried 9mm automatics . . . here was McVey with a six-shot Smith & Wesson. A six-shooter! Retirement age or not, McVey was - mon Dieu! - a cowboy!'' The third strand of the plot involves an international organisation that has a master plan of apocalyptic dimensions and whose influence extends everywhere. They are Nazis, experimenting with atomic surgery and waiting for their time to come around again: ''Fur Ubermorgen - for the day after tomorrow.'' They have genetically engineered two perfect Aryan twin brothers, at 24 years of age the finest physical specimens alive. Osborn's love interest is Vera Monneray, whose life is complicated because she is having an affair with the French prime minister, Francois Christian. She is a young and beautiful trainee surgeon, which is fortuitous, because when Osborn is fished out of the Seine with a bullet in his hamstring, he needs someone to operate on him without telling the police. It is this patness that lets the book down. Osborn is crippled by a bullet in his leg, but his lover has surgical skills. The ruthless assassin hunting Osborn is identified by witnesses as tall, so the police call him The Tall Man. In fact his legs have been amputated and he uses artificial limbs to disguise his height. Such convenience is the most overworked in the thriller writer's armoury and spoils what might have been an enjoyable, if conventional and tortuously long, book. The plot does not justify the length and the length does not do justice to the overstretched plot. The Day After Tomorrow leaves one feeling not thrilled, but incredulous, right up to the standard denouement on the Jungfraujoch mountain. Everything is revealed, nature plays its part - symbolically and in reality - and good conquers evil.