If you consider that Sudoku is a stroll in the park, and Killer Sudoku no more than a jog round the block, you might still regard this puzzle as a marathon. It is not something to be undertaken lightly.
Having given the warning, it is important to note that the interactive features of the puzzle can provide you with some assistance, if required. Click on Help in the puzzle window to find out more.
Each puzzle is available to play online for two weeks from its date of release. If you run out of puff before completing the puzzle, use the Save function to store the incomplete puzzle.