Rules
The Knight’s Tour is a classic chess puzzle. You move a single knight around an empty board and try to land on every square exactly once. The Devil’s Plan used it as a hidden stage, with three boards to clear one after another: 6x6, then 7x7, then 8x8.
Moving the knight
The knight moves in an L shape: two squares in one direction, then one square to the side. From the middle of the board it has up to eight moves. Near the edges and corners it has far fewer.
Visiting squares
Every square the knight lands on is used up. It cannot land there again, although it can jump over it. The tour is complete when every square has been visited once: 36 squares on 6x6, 49 on 7x7 and 64 on 8x8. If the knight has no legal move left before the board is full, the attempt fails.
On the show
Clearing all three boards won 10 Pieces. Failing cost the player all their Pieces except one, but did not eliminate them. Only one player could take on the challenge each time it was found.
Our version
- You choose the starting square. On 7x7 the start must be on the corner colour, which has 25 squares against 24 of the other colour.
- Legal moves are highlighted and visited squares are numbered.
- Challenge: 6x6, then 7x7, then 8x8, with one 10-minute clock for all three. No undo and no hints. If you get stuck, you can retry that board while the clock keeps running.
- Practice: any board from 5x5 to 8x8, with undo and a hint button.
- Daily: an 8x8 board with a fixed starting square, the same for everyone each day. Your score is your time.
Strategy
Go where the options are fewest. Before each move, count how many onward moves each target square would have, and pick the lowest. This is Warnsdorff’s rule, and it is the single best habit for this puzzle.
Clear the edges early. Corner and edge squares have only two to four ways in. Leave them for later and you will find them cut off with no way to reach them.
Corners are traps. A corner square has only two neighbours. Once you have used one of them, make sure the other is still free to get in or out.
Start near a corner. Starting in or next to a corner deals with the hardest squares first, while the board is still wide open.
Spend practice time on 7x7. The odd board is the one with the colour rule and it tends to catch people out. Getting comfortable there saves time in the challenge.
Do not panic on a retry. In the challenge the clock keeps running, but a calm second attempt using the fewest-moves rule is usually faster than a rushed one.