Secret Agent: an original card game by David Parlett

The point of this otherwise ordinary trick-and-trump game is that you score the number of tricks you win yourself multiplied by the number won by another player who is your Secret Agent. If you are your own Secret Agent, you score the square of the number of tricks you win. Only you know who your Agent is, but (unless you are your own Agent) you don’t know the identity of your Runner (the player whose Agent you are), except in so far as you may infer it from the play.

Cards: Use a standard 52-card pack ranking AKQJT98765432 in each suit. You also need four "assignment cards", indistinguishable from the back, marked respectively Left, Opposite, Right, Self. For this purpose you might use four Aces from an old pack, with suits indicating identity thus: hearts = Left, diamonds = Right, clubs = North, spades= Self.
Deal: All play, including the turn to deal, passes to the left (clockwise around the table). Deal 13 cards each, face down and one at a time. Then find some way of shuffling the assignment cards and dealing them face down, one to each player.
Appointing your Secret Agent: Your assignment card tells you who your Agent is. Left (hearts) means your immediate left-hand neighbour, Right (diamonds) your immediate right-hand neighbour, Opposite (clubs) the player sitting opposite you, and Self (spades) means yourself.
Trump-making: Each in turn, starting with the player at dealer’s left, announces which suit they forbid to be trump. The first three forbidden suits must all be different. The fourth player then either appoints the remaining suit trump or decrees that the hand be played at No Trump.
Play: Dealer’s left-hand neighbour leads to the first trick. Normal rules of trick play apply. (You must follow suit if you can, but may otherwise play any card. The trick is taken by the highest card of the suit led or by the highest trump if any are played, and the winner of each trick leads to the next. Stack tricks face down and squared up so that everyone may always see how many everyone else has already taken.)
Score: At end of play you each reveal your assignment cards to show whose score to multiply your own by. Then do the multiplication, note your own score, and carry it forward towards a cumulative total.
Exceptional score: If you lose every trick (misère), your own multiplier is not zero but 10. Thus if you drew “Self” you would score 100; if not, your runner(s) will also have their score multiplied by 10.
Game: The winner is the player with the highest cumulative score after four deals. To break a tie, play one or more additional deals.
Note: It isn’t possible for each player to have a unique Secret Agent. At least two players, and possibly even all four, will be running the same one. For example, if South’s agent is Self, West’s Right, North’s Opposite, and East’s Left, then everybody will multiply their own number of tricks by South’s!
Sample scores: Given the flattest distribution of won tricks, 4-3-3-3, an individual player may score 16, 12 or 9 points. Given the spread 5-4-3-1, an individual may score 25, 20, 16, 12, 9, 5, 4, 3 or 1. If one player wins all 13 tricks, the possible individual scores are 169, 130 and 100, variously partitioned.