The King of Hearts Has Five Sons is a game of deduction where the goal is to guess a secret phrase which is represented by the identities of two hidden cards.
The game is played with the 12 face cards of the standard deck along with either 10 number cards (for 4 or 5 players) or 8 number cards (for 3 or 6 players). For 4 or 5 players, the number cards used are Ace through Ten of Hearts. For 3 or 6 players, the number cards used are Ace through Eight of Hearts.
One face card and one number card are drawn at the beginning of the game and placed face-down. These two cards represent the secret phrase the players try to guess. The remaining cards are shuffled together and dealt to the players.
The secret phrase is of the form "[person] has [number] sons." The person is represented by the secret face card, and the number is represented by the secret number card. For example, if the secret face card is K and the number card is 5, then the secret phrase is "The King of Clubs has 5 sons." The Ace of Hearts represents the number 1.
The game is played in rounds. In each round, each player has the chance to ask another player to reveal a card. The question is phrased as a statement of the form "I think [person] has [number] sons."
For example, if Player 1 wants to know whether Player 2 has J or 2, Player 1 will say to Player 2, "I think the Jack of Spades has 2 sons." How Player 2 responds depends on whether they have one, both, or none of the cards:
In the first and second cases above, Player 1 is not told whether Player 2 has the other card that Player 1 asks for. In addition, the other players do not see which card Player 2 shows to Player 1. All they know is that Player 2 has one of the two cards Player 1 asks for.
At the end of each round, each player submits a guess which is not seen by other players. Whoever submits the correct guess wins the game. If no one is correct, another round is played. The game continues until someone makes a correct guess.