"Barker and Llewelyn receive in the mail an unexplained key stamped with the letter Q. Barker, recognizing it for what it is, uses the key to unlock an anonymous door in the alleyway, which opens to an underground tunnel leading to Downing Street. The Prime Minister has a small task for Cyrus Barker. A Foreign Office agent stole a satchel in Eastern Europe, but was then himself murdered at Charing Cross. The satchel contains a document desperately wanted by the German government, but while the agent was killed, the satchel remains in English hands. With a cold war brewing between England and Germany, it's in England's interest to return the document contained in the satchel to its original owners and keep it out of German hands."