The object of the puzzle is to get the white knights and the black knights to exchange their position – white on top corners and black at the bottom corners. Knights move in an L-shaped path.

white 9 to 2 – black 1 to 8 – black 3 to 4 – white 6 to 1 – black 4 to 9 – black 8 to 3 – black 3 to 4 – white 2 to 7 – white 7 to 6 – black 9 to 2 – black 2 to 7 – black 4 to 9 – white 1 to 8 – white 8 to 3 – white 6 to 1