Killer Sudoku (the Guardian)
The Guardian

Test your wits against 210 difficult previously unpublished killer sudoku puzzles in the first book in the new Guardian puzzle book series.

The Guardian's killer sudoku puzzles are enjoyed by hundreds of thousands of people every day. While only a minimal level of mathematical knowledge is needed, all of your logical reasoning will be required to solve these brand-new puzzles. The puzzles have been designed to increase in difficulty as the book progresses, meaning this book can be enjoyed by novice and master alike.