What is the person sitting opposite you in a crowded train engrossed in: a Dan Brown thriller, the last Harry Potter novel, a complicated text message, a crossword puzzle? No. They're caught up in the greatest craze to strike Britain in many years: Sudoku. Sudoku is a number-placement puzzle played on a square grid. To be successful, a player needs patience and an aptitude for logic (which playing the game helps to develop). You do not need to be good at maths, or a genius at crosswords; you do not need ever to have played the game before. What you do need, though, is The Little Book of Sudoku , a genuinely pocket-sized book that contains an astonishing 150 puzzles of five levels of difficulty and (for those who need a little help), their answers. Sudoku is completely addictive and has been sweeping the nation since the first puzzle appeared in a newspaper late in 2004. Specifically commissioned for the book, and created by an expert in both logic and artificial intelligence, the 15...