This is a distant relative of Battleship. Each player deploys four agents over a world map. Then, using probes you try to deduce the position of the enemy agents before he deduces the positions of yours. Basically, when you probe a grid location, the opponent announces how many of his agents can be reached in a straight line (including diagonals) from the probed location --excluding any of his agents which may be hidden behind others. Some extra complications occur because both are playing on the same map: for example, you may not probe where the opponent has probed, which opens up strategic opportunities... "Checkpoint: Danger!" is what you call out when you're convinced one of his agents is in the same location as one of yours.