Die Vierde Kabinet revolves around corruption in the police and the Organised Crime Unit, the hated internal investigation unit of the police who set traps for and spy on other police units to try and uncover corrupt members.

The same corrupt police attempt to turn the tables by trying to find information about who is in this specialised unit.

In 1993, shortly before the first democratic election in South Africa, a group of policemen rushed to get rid of files containing information about illegal police operations.

The files were placed in filing cabinets, taken to a secret place and destroyed with explosives. But in the atmosphere of panic and disorder a cabinet - the so-called "fourth cabinet" - got lost and was forgotten.

In 1997, Bonnie Badenhorst (Vanessa Pike), a policewoman attached to the special police unit investigating corruption, discovers the cabinet. Badenhorst, whose brother died in Angola, decides to remove the cabinet and hide it without informing her colleagues.