P.I. is a deduction game for two to five players. Each player is competing to be the best private investigator in the city. A full game is made up of three 'mini-games'.
In each mini-game players must attempt to solve their case by finding the suspect, the crime they committed, and the location where they are now hiding out. The twist is that players are attempting to solve the case held by the player to their right, with the fastest investigators earning more points than the slower ones.
A mini-game starts with the board being seeded with Suspect and Crime tiles. Each player takes one Suspect, one Crime, and one Location card from the 'Case' decks. This set of three cards is the case that the player to their left must solve. Nine Evidence cards are now turned face up and placed by the side of the board.
When it is your turn you can do one of three things. You can place one of your Investigator counters, or select an Evidence card, or attempt to solve your case.
Placing an Investigator piece in a location gives you information on all three tiles there. The player to your right looks at the Case cards they hold.
If a Case card matches one of the tiles in the location then they will tell you to place one of your discs there. If a Case card matches one of the tiles in an adjacent location then they will tell you to place a cube.
The discs and cubes you place are not assigned to any one tile. Thus, if you are told to place a disc in the location then you know one of the three tiles in the location matches one of the Case cards, but you do not know which one.
If you take an Evidence card then the player to your right tells you whether you need to place a disc or cube. The main difference from placing an Investigator is that if you do place a disc or cube, then you place it on top of the tile that matches the Evidence card.
Finally, once you think you have worked out all of the elements of your case you can make an attempt to solve it. If you are correct then you score points, depending on how many other players have already solved their cases. If you are wrong then you suffer penalty points.