Codenames Duet keeps the basic elements of Codenames (give one-word clues to try to get someone to identify your agents among those on the table), but now you're working together as a team to find all of your agents.
To start, lay out 25 word cards in a 5x5 grid and place a key card in the holder so that each player sees one side of the card. Each player sees a 5x5 grid on the card, with nine of the squares colored green (representing your agents) and one square colored black (representing the assassin). The assassin is in different places on each side of the card, and three of the nine squares on each side are also green on the other side! Working together, you need to reveal all fifteen agents (without revealing either assassin or too many innocent bystanders) before time runs out in order to win the game.
Codenames Duet is recommended for 2 players, ages 14 and up.