Continuing the popular Overworked & Underpuzzled series, Killer Sudoku contains almost 200 tricky puzzles requiring a certain amount of logic and skill to solve. Killer Sudoku is often seen as the most challenging Sudoku, and so this is the perfect puzzle book for anyone who loves to be tested during their coffee break. With nearly 200 puzzles, this is a tricky collection perfect for anyone who works too hard and likes to reset their mental faculties with a classic logic test.