VIETNAM VET John Rain has been killing people for more than a quarter of a century. So his creator, Barry Eisler, says it's time he hung up his knife and pistol. The assassin, Eisler says, will come full circle in his sixth outing. All he has to do is get the manuscript to his publisher by deadline. 'Yeah, I'm getting there,' says Eisler in Tokyo, a city his Japanese-American serial hitman knows well. 'It's never easy to write. I don't know of a writer who at some point hasn't had to grapple with the task. A novel requires a lot of hard work and requires you to constantly ask yourself why, when, where, who and how.' Rain is drawn from Eisler's own life. 'I've been lucky to have lots of different experiences that build up in my mind and take on a life of their own. I've always been interested in books about assassins, I've always had an interest in martial arts and what might be termed 'forbidden knowledge', and when we lived in Tokyo in 1993 and 1994, I fell in love with the city,' says the American who now lives in San Francisco but travels to Japan and around Asia. Eisler's fascination with 'forbidden knowledge' took root as a child when he read the words of a cop in a biography of Harry Houdini: 'It's fortunate that Houdini never turned to a life a crime, because if he had he would have been difficult to catch and impossible to hold.' Eisler was hooked, the realisation that someone could acquire knowledge that made them dangerous leading to a lifelong study of martial arts. His library extends to books on such esoteric subjects as methods of unarmed killing, lock picking, breaking and entry, and spy craft. Eisler joined the CIA's Directorate of Operations straight out of law school. There he underwent paramilitary and espionage training, and learned Japanese. Frustrated after three years without an overseas posting, he returned to law and became in-house counsel at the Osaka headquarters of Matsushita Electric. He took the opportunity to further his study of martial arts and later moved to Tokyo. 'Tokyo catalysed everything into the person that is John Rain, and [my first book] Rain Fall,' he says. 'It's no coincidence that he likes single-malt whisky and jazz music.' Requiem for an Assassin, to be released in the US in June, will almost certainly be Rain's final outing in print, although Barrie Osborne - who won an Oscar for producing the Lord of the Rings trilogy - has taken an option on the movie rights to the series and 42-year-old Eisler recently turned Rain Fall into a screenplay. He says he's come a long way since beginning Rain Fall - which took nine years to get into print - in 1993. 'When I started, I had no deadlines and no affirmation from anyone; when I'd had a busy day at work, came home to my wife and daughter and was tired and would rather turn on the television, it wasn't always easy to motivate myself to write,' he says. 'The thing that helped me, I found, was the fear of how I would feel if I never finished the book. That was what kept me writing: that one day I'd look back and say to myself, 'I wonder what would have happened if I'd written that book'.' Sticking with it has paid off. There have been five John Rain books, sales are around one million copies and Chinese-language editions are planned. Eisler says he has no intention of giving up writing to return to his previous line of work. Rain has ranged far and wide across the region, with frequent visits to Hong Kong. Killing Rain, the fourth book in the series, saw the protagonist involved in a shoot-out with a gun-runner in the Long March Bar at the China Club. Meticulous in his attention to detail, Eisler visits all the venues he uses in his books and had the idea for Rain to hide in a cleaner's closet in the toilet at the club after paying it a visit himself. He even took photos. And while some characters in the genre never age - James Bond's looking awfully good for a man who got his licence to kill in 1952 - Eisler wants Rain to grow older. 'Part of what's interesting in The Last Assassin and the new book is that Rain does age,' he says. 'He's not as fast as he used to be and he needs to use new tactics. His outlook is different.' Eisler, who has completed a book a year since taking up writing full-time in 2002, says Rain's final journey will take him from Vietnam to Bali, Paris, New York, San Francisco, Amsterdam and, naturally, Tokyo. 'I still don't know how it will end but I won't kill Rain off. That would be a cheap way of avoiding the questions of whether there's a consequence of all the violence he has caused and whether there's the opportunity of redemption.'