The game set in the United Kingdom, where the player is the director of a secret governmental agency involved in clandestine domestic operations; the headquarters is hidden on the thirteenth floor of a bank building in London Docklands, hence the title.

The player takes on the role of the Director General of the "Department of Agriculture and Fisheries", a non-existent executive agency that conceals a secret police which keeps the government popular by any means necessary.

Answering only to the Prime Minister, the Director General has the power to use wiretapping, surveillance, smear tactics, disinformation, burglary, kidnapping, torture, and assassination to keep the government popular with the people.

Each individual or group is rated in the reports as to prominence, power, and orientation towards the government, attributes that will affect the likelihood of success of attempted actions taken against them and the likely results on public opinion.

Beyond disliking the KGB or Gestapo-like "loathsome secret police activity" the game depicted, he wrote of the gameplay that "Hannah Arendt could not have conceived of more banal evil.