In Voices In My Head the players find themselves in the courtroom and in the mind of a man on trial for robbing a bank. One player takes on the role of the prosecutor trying to convict the defendant, Guy, and send him to prison; everyone else adopts aspects of Guy's personality, such as honesty or selfishness, and tries to influence the process. To win the game, each player must achieve their hidden goal.

Each round the prosecutor plays a trial card to present evidence or call witnesses. Players then attempt to control Guy's actions by placing control markers on a three-dimensional game board representing his brain. These actions will influence the jury in several ways and ultimately determine whether Guy is released or sent to prison.