The Little Book Of Sudoku 3 (2016)

But this time, it's deadly serious: 201 fiendishly difficult puzzles in five excruciatingly advanced levels, for the really skilled and dedicated Sudoku fan.

 

Addicts everywhere will welcome the third volume as it challenges the parts that other puzzles cannot reach. The super difficult puzzles inside will tax the most agile Sudoku brains - and leave many people begging for mercy . . .