There's a public grid of Codenames cards visible by everyone. It might be 4x4 or 5x5. Each round, two players A and B try to communicate one of the cards' identity to each other cryptically without the other players working out which card it is.
In a conversation between A and B: They collectively secretly determine some shared secret to be their private Key for this conversation. Initial experiments suggest one Articulate card might be about right.
A privately rolls the "row" red d6 for their Target; B privately rolls the "column" green d6 for the Target. They mustn't reveal these to each other or anyone else.
Now they have a spoken conversation trying to clue each other into the Target /without/ any of the listeners guessing the Target. The idea is they make cryptic references to their Key that hopefully nobody else will follow.
What's allowed in the conversation:
References to the semantics/meaning of their private Key and the words on the grid are good. "My row contains something you'd find in the Nature location." GOOD.
Positional clues are not allowed. "The thing that you'd find in the Nature location? Go one row left from that." BAD.
References to individual letters are not allowed. "My row contains something that starts with the same letter as the Nature location." BAD.
Anything that could be described as "encoding" is not allowed. "Okay, if the cards in the grid have numbers 0-15, then calculate..." STOP RIGHT THERE.
Syntactic clues are frowned upon. "My row contains something that starts with the first half of the Nature location and ends with something that sounds like the Action." DUBIOUS.
Then everyone submits a secret guess as to the Target. Each correct "outsider" gains points themselves and reduces A and B's score. (Possibly you guess the row and column independently and score them separately.)
I think the scoring might be something like:
Each player starts off with a few points. When A and B roll the dice (A determining a row, B determining a column), they each pay one point to the middle. After their conversation, all players (A, B, C, D, E) reveal their guess for the Target. Then:
A was cluing the row.
If B got the row right, B takes 3 points from the middle and gives 1 to A
If C got the row right, C takes 1 point from A
Ditto D, E
B was cluing the column
If A got the column right, A takes 3 points from the middle and gives 1 to B
If C got the column right, C takes 1 point from B
Ditto D, E
Score once more for the precise Target (i.e. row and column both correct)
If A and B both got the Target right, they take an extra point each from the middle
If C got the Target right, C takes an extra point from the middle
Ditto D, E.
Examples of how this works out in practice:
A and B are both too blatant - Everyone got everything right.
A pays 1, gets 4 from middle, but gives 1 each to CDE; net +0
B pays 1, gets 4 from middle, but gives 1 each to CDE; net +0
C gets 1 from A, 1 from B, 1 from middle: net +3; ditto D, E
A and B are both too cryptic - Nobody got anything right
A pays 1, net -1
B pays 1, net -1
C gets +0; ditto D, E
A and B are perfectly in tune - A and B got everything right, C, D, and E got nothing right
A pays 1, gets 4 from middle, net +3
B pays 1, gets 4 from middle, net +3
C gets +0; ditto D, E
A and B are perfectly in tune, but C understands - A, B and C got everything right, D and E got nothing
A pays 1, gets 4, gives 1 to C, net +2
B pays 1, gets 4, gives 1 to C, net +2
C gets +3
D, E +0
A is too blatant, B is too cryptic - Everyone got the row right, nobody got the column right except B
A pays 1, gets 1 from middle, gives 1 each to CDE; net -3
B pays 1, gets 2 from middle; net +1
C gets 1, net +1; ditto D, E
A is too blatant, B is just right - Everyone got the row right, only A+B got the column right
A pays 1, gets 4 from the middle, gives 1 each to CDE; net +0
B pays 1, gets 4 from the middle; net +3
C gets 1, net +1; ditto D, E
A is just right, B is too cryptic - A+B got the row right, nobody got the column right except B