In Agent Doppelnull each player has ten numbered secret agents, plus ten cards (also numbered) of the other player's color. Before the game, each player places her agents in a row so that the numbers are hidden from the opponent, then the opponent removes three of these without looking at them.
Afterwards, each player openly places her seven cards in front of the opponent's agents. The owner of the agents then moves each agent on top of the card next to it: If the number of the agent is higher than on the card, it is placed on the "+" symbol; if it is smaller, on the "-" symbol; if the number matches, the agent is laid down flat.
Taking turns, the players now remove a card from the opponent's row and replace it with a card from their hand; the owner of the agent has to reveal "+" or "-" again or lay down the agent. This is repeated until a player has identified all of the opponent's agents, thereby winning the game.