The board is simple and the missing line is vital. Two players each have two counters of different colours or markings to the other player, here we have used red and yellow, and the starting position is shown above.

Either player may start and moves are made in turn. A counter can only be moved along a line to a free circle and no jumping is allowed. The loser is the first player that can not make a move.

At first it may seem that the game goes on and on but the trick is to catch your opponent with both counters on one side and place your counters so they cannot move.

I have seen this game end in three moves or last for hours until someone makes a mistake.   Try it for yourself.