In Private Investigator you are Dick Slammer, a famous PI specializing in Adultery cases. One day Dick is visited by Nancy who claims her husband is cheating on her and asks to investigate. Dick takes on the mission, while Nancy awaits him in his bedroom.
Private Investigator is a side-scrolling arcade-style action game. You need to navigate maze-like stages, collecting keys and items, punching or shooting bad guys and avoiding hazards. In each stage there are hookers, and Dick can have sex with them, gaining weapons, ammo, health refills and other valuable items. At the end of each stage Dick finds Nancy's cheating husband and must capture him on camera to finish the stage. Completed stages unlock new adult toys for Nancy to play with in Dick's bedroom in FMV sequences.
The game's main menu is Dick Slammer's office in full 3D with 360 degree rotation. Aside from doors leading to the helipad (actual game missions) and to the bedroom there are various objects that can be interacted with: moose head tells jokes, the skeleton recites quotes of famous people, the TV shows a bunch of adult video clips, the computer contains adult magazines, telephone lets you listen to some sex talk, and the CD player allows to change audio options.
All adult material is licensed by adult multimedia company Private, hence the title of the game. The CD also contains a demoversion of PornMine -- an adult clone of Minesweeper and advertisements of other products by Image Line and Private.