For the most varied range of sudoku puzzles with the widest range of difficulty available anywhere, look no further than the Observer's Killer Sudoku. Combining elements of sudoku and kakuro, these headscratchers will test the skills of even the most practised sudoku fan. This collection contains 150 previously unpublished puzzles of varying levels of difficulty, so whether you're new to the Killer Sudoku grid or are a seasoned solver looking for a challenge, this book will keep you occupied. Be warned, though - some of these puzzles are so fiendishly difficult they may well keep you up all night.