Britain is well and truly hooked on Sudoku, the logic puzzle par excellence.
Supersudoku is a fiendish variation, with sixteen grids instead of the usual nine.
It's much more difficult to complete, and has won legions of fans in the Mail on Sunday.
Mail on Sunday Supersudoku is the first ever book of Supersudoku puzzles, and contains 300 mind-bending pages of Supersudoku from the paper's own puzzlers.
If you're hooked on Sudoku and are looking for the next challenge, get ready - this won't be easy!