Like the standard sudoku, the object of the puzzle is to fill in the whole 9x9 grid with numbers 1 through 9 so that each row, each column, and each of the nine 3x3 squares must contain all the nine different numbers.

There are special clue-numbers placed on the border lines between selected pairs of adjacent squares of the grid. Each clue-number is the difference between the two numbers that should be in the respective pair of the adjacent squares just next to left & right (or right & left) from that clue-number.

For example, a clue-number 7 on the border line between two adjacent squares means that possible pairs of numbers for these squares can be from the following combinations: 1 and 8; 2 and 9; 8 and 1; or 9 and 2.

As the puzzle has two sets of solutions, the readers are required to get an additional clue from the following story to pick the "correct" solution.

It was a day of joy in the kingdom of Fictusia when the 18-year-old prince married his longtime childhood friend. As the prince and his bride entered the palace garden where the grand wedding ceremony was held, a voice rang out among the guests: "Now is the time to settle our old score!"

The king and queen were stunned to see an old woman walking slowly towards them. Although old and haggard, they could still recognize her as the witch who intruded upon the prince’s birthday celebration eighteen years ago. At that time, she was a beautiful young woman, carrying a baby girl in her arms and asking them to let her daughter – the baby girl – to be their future daughter-in-law. The king and queen still remembered vividly the anger on her face as they rejected her request. Before she disappeared in a gust of wind, she vowed to return one day to settle the score. Since then, many years had passed, and the king and queen had almost forgotten about the intrusion of the unwelcome guest.

By now, the unwelcome guest was standing once again in front of them. The king asked her: "What do you want?" The witch laughed loudly: "Today will be the saddest day for the royal family of Fictusia. Your son will marry none other than my daughter."

Before the king could say anything, the witch vanished in a gust of wind. Everybody rushed for cover. When the calm returned, they discovered that many trees had been uprooted by the powerful wind. Tables and chairs were overturned. Food, bowls, plates and all other things were scattered all over the place. It came as a shock to everyone in the palace that the bride was missing! They searched the whole palace but they found no trace of her.

The prince was very anxious to find back the bride. He and two warriors rode out of the palace at once to look for the witch who was believed to be hiding in the mountainous border regions.

After travelling for many days in the rugged terrain, they were hungry and thirsty. The prince sent one of his men to look for wild fruits and water in a nearby forest. The man rode towards the forest, but failed to return after a long time. The prince sent the other follower to look for the first man. After waiting for a long time, he decided to enter the forest look for them. With a swing of his whip, he sped towards the forest on his horse.

Not very long after, he realized that he had lost his way in the forest. He could not find his way out of the forest, which seemed to be a maze to him. Suddenly he spotted a figure sitting under a tree in the distance. As he approached the figure, he found that it was an old man. The old man told him that he had fallen and hurt his legs while picking wild fruits. He asked the prince to bring him back to hut.

Without hesitation, the prince got down and lifted the old man onto his horse. As he led the horse, the old man showed him the way to his abode. After sometime, they reached a small hut. The old man said: "Thanks very much for bringing me home. Here is something which will help you to find your way out of the forest." The old man handed him three pieces of paper. On one piece of paper, the young man found a 9x9 grid that looked like a Sudoku puzzle.

The old man explained: "This puzzle has a set of two solutions which can be found on the other two pieces of paper. On the piece of paper with the ‘correct’ solution is a map that would lead you all the way out of the forest. However, if you fail to solve the puzzle and choose to follow the wrong map on the piece of paper with the ‘incorrect’ solution, you will end up in disaster. The top part of the puzzle, the solutions and the maps are assumed to be facing the northerly direction. As you traveled along the way, you may find some strange features that will have some semblance with the ‘correct’ solution of the puzzle."

The prince thanked him and bid him farewell. As he was going to leave, the old man called him back, saying: "Wait, young man, I have nearly forgotten to tell you something. Don’t bother to look for your followers. The first one was so selfish that he had ignored the call for help from a fellow countryman in distress. As punishment for his selfishness, he was devoured by the Beast of the forest. As for the other man, he was foolish enough to use the wrong map and ended up in the stomach of the Beast of the forest. Follow that path on the right and you will find some strange features on the way to guide you out of the forest."

After he finished talking, the old man vanished gradually in a roar of laughter before the prince. The prince was stunned by the scene of the old man disappearing gradually in the thin air. He was sad to hear the news of the deaths of his two followers. With a swing of his whip, he rode towards the path on the right.

After travelling for sometime in the forest, he came to a square pond in the middle of a clearing. Feeling very tired, he got down from his horse and sat down beside the pond for a rest. Suddenly, he remembered the piece of paper with the puzzle. He took it out of his pocket and tried to solve it. Sure enough, he found that it had two sets of solutions, which were similar to the solutions on the other two pieces of paper with the maps of the forest.

Taking a careful look around him, the prince found some strange features around the pond. Near the four corners of the pond, he found a single rock, two rocks, three rocks and four rocks respectively in the clear water of the pond. At the edge of the pond, he also found one plant, two plants, three plants and four plants growing near the single rock, two rocks, three rocks and four rocks respectively.

The young man studied the solutions on the two pieces of paper carefully. Realizing he had found the solution, he got on to his horse and found his way out of the forest with the correct map.

Dear readers, can you find the solution too?

Henry Kwok 2007-12-23