Times Ultimate Killer Su Doku Book 2 (HarperCollins Publishers)

For those who like to live dangerously and push beyond their mental comfort zone, steel yourself for the second book in The Times' toughest Killer series yet. Prepare for the extreme mental challenge of 100 Deadly-level Killer puzzles, including, exclusive to The Times, 20 Extra Deadly, to really test your limits: this is the only series in which you'll find such a torturous collection. The Times Ultimate Killer Su Doku 2 is not for the fainthearted. The puzzles use the same 9x9 grid as Su Doku, and have an added mathematical challenge. The aim is not only to complete every row, column and cube so that it contains the digits 1-9, it is also necessary to ensure that the outlined cubes add up to the same number as well. If the first Ultimate Killer Su Doku didn't scare you off - see how you fare after tackling this one...