Just when you thought it was safe to pick up a pencil

Killer Su Doku is based on the original Su Doku grid, with the same rules and numbersâ€”1 to 9â€”but with an added deadly twist. This time there is an element of arithmetic involved and there are few, if any, clues. The aim is to not only complete every row, column, and cube so that it contains the digits 1 to 9, but to also fill in the outlined cubes so they add up to the same number.

Hints to solve the puzzle are hidden in the joined squares where only one combination of numbers applies. In the case of joined squares, if the printed number is 3, it should be 1 and 2 that go into the squares. Likewise, in the case of three joined squares, if the printed number is 6, the only combination possible is 1, 2, and 3.

To add one final fiendish level, each puzzle also has a time worked out by its Japanese creators so you can try to beat the clock.

Spotlight customer reviews:

Customer Rating: Summary: Better than regular Sudoku Comment: I encountered Killer Sudoku in a Will Shortz sudoku variants book and became hooked on it, and this is a great book of it. It allows you to move between a variety of solving techniques taken from both regular Sudoku and Kakuro. The puzzles here come in a good variety of solving difficulty, with enough easy ones for you to practice your techniques on, and enough challenging ones that you won't get bored. Customer Rating: Summary: Solid and fun Comment: I ran into Killer Sudoku accidentally, and became hooked ever since. The (simple addition and subtraction) math involved adds a new dimension to the puzzle. Unlike the standard Sudoku, Killer Sudoku puzzles have more twists and surprises waiting to be explored. The more difficult puzzles in this book are very satisfactory in harboring many pleasant and exciting ones.

The books contain 110 puzzles of 5 levels. When you advance to the last two level, your skill and fun are elevated as well. I guess after you mastered the game, you may want to get books with only difficult ones (and they should be so published). One nice thing about this book is that the puzzles seem to have been tested, and there is a 'par' time for each one of them. For easy one the pars are ten to 20 minutes, and the hardest ones up to 90 minutes. These par times are pretty good in that I tended to exceed them in the beginning, but after I have advanced to high levels and came back to do some easier ones that I skipped I often beat the par. The time competition factor also is a way to enjoy the easy ones.

Highly recommended for going through the levels and mastering the game. If you are looking only for tough Killer Sudoku books, this one contains about 20 very good ones. Customer Rating: Summary: A must for the Sudoku bored Comment: If your bored of Sudoku and not finding the standard puzzles challenging you need to try these out. The page layout of this book is good there is ample room to write your number combinations and there are suggested times for each puzzle. The paper used in the book is softer but stands up fine to an eraser.

Customer Rating: Summary: Plenty of fun Comment: I do enjoy regular Sudoku. But there are a couple of problems with it. First, while it uses numbers, it in no way uses the properties of numbers. Second, the level of effort to solve such puzzles is generally uneven; you may get a few numbers early, but then it gets very tough, and soon after that it is easy again. When it is tough, you may have to write down possible values in a square or guess, and that's unsatisfying compared to being able to simply write down correct numbers in blank squares.

With Killer Sudoku, one does get to use the additive properties of numbers, so there really is a difference between the symbols! And the level of effort is more nearly even. In addition, even hard puzzles generally can be solved without writing anything down but the answers. It is my favorite Sudoku variant ("Greater than Killer Sudoku" is my second favorite).

This book is about at the right level. Do not be scared by the "deadly" puzzles at the end, as I found them to be easier than some of the earlier ones.

I recommend this book to all those who enjoy a challenge and have some time on their hands. Customer Rating: Summary: Lots of Fun Comment: In my opinion, Killer Sudoku puzzles are much more fun and satisfying to solve than regular Sudoku puzzles because of the added complexity of the sums and the various techniques that can be employed to solve them. "Killer Su Doku 1: The Deadly New Dimension" contains 110 puzzles of which there are 17 Gentle, 30 Moderate, 42 Tricky, 16 Tough, and 5 Deadly puzzles. Each puzzle has a suggested time to beat. There is also a two-page "Guidelines for Solving Killer Su Doku".

I didn't find the guidelines for solving to be particularly useful. They give a quite minimal explanation of how to solve these types of puzzles and leave out explanations of some of the more important techniques for solving, such as the 45 Rule. (Steve Arons book, "The Official Book of Killer Sudoku" contains a much more comprehensive introduction.)

Regarding the suggested times, I didn't specifically time myself, but I often noticed that I took much less or much more time than what was suggested. As for difficulty, I found that sometimes a puzzle in a given section was either much harder or much easier than what was implied. The puzzles in the Deadly section were no more difficult than the ones in the Tough section. The hardest puzzles in the book are 78, 98, and 105. I eventually figured out some interesting equations and relational techniques for solving 78 and 98. (Whew, that was fun!) Puzzle 105 is the only one that I have not yet managed to solve.

This brings me to a recommendation for the Solutions section. In general, I find the solutions in the backs of Sudoku books to be useless. If I finish a puzzle and it conforms to the rules then it's correct; otherwise it's wrong. I don't need a solution to tell me that. The only time I look at the solution is occasionally when I'm doing a really difficult puzzle and I want to check an intermediate result to make sure I'm on the right track so I don't end up having to erase the entire puzzle and start over. This also helps to instantly understand what type of mistake I made. Something that would be really helpful in the solutions for the really difficult puzzles would be to show a partially solved grid and an explanation of how to get to the next step.

On the whole I found this book to be very enjoyable and highly recommend it for any Killer Sudoku fan. Publisher, another one please!