Su Doku is the classic number puzzle.

The Times Su Doku Book 13 contains a mix of 150 mind-bending variations, ranging from mercifully Mild to the uber-challenging Super fiendish:

10 Mild puzzles
60 Difficult puzzles
50 Fiendish puzzles
30 Super fiendish

This latest edition offers completely new and unpublished puzzles, provided by the puzzle suppliers to The Times, and are of the highest quality.

So sharpen your wits and prepare to get solving – the only question is: can you make it to the end?