Copyright (c) 1995 Eric Remy

The game is played on a 9x9 torus board (i.e., there is no edges).

TURN - At each turn, each player can do one of two things:
MOVE - A stone can move to an adjacent empty cell (in any orthogonal direction).
DROP - A wall can be dropped into an empty cell. 
GOAL - The first player which has his stone surrounded by walls, looses. If a drop of a wall surrounds both stones, the game is a draw.

I would include to the original rules, that a stalemate is a loss, since it may occur that both stones are trapped inside a mutual area, and if adjacent to each other, they may never be surrounded just by walls!

An example

If White play at d2, Black must move c2-c3, to avoid defeat.

Cell c3 is a seki point, i.e., both players would loose if they placed a wall there.

There is a similar game, called Entrapment designed by Rich Gowell, more complex and probably more stable. There are three stones, called Roamers, with more freedom of movement. Check the full rules. There is also a Zillion's ZRF to play Entrapment. Another similar variants are Alcazar, Blockade, Cul-de-Sac and Quoridor.