The Doctor arrives on New Memphis, specifically, a spaceport known as "Elvis the King Spaceport" which has grown into a vast city-state. It is set to open Terminal 13, but problems develop, and the Doctor faces a lockdown situation. A notorious criminal, the Invisible Assassin, is at large, and Judoon troopers are sent to apprehend him. The Doctor partners with a Judoon Commander and a teenage private detective named Nikki Jupiter. This last character is an homage to the TV series Veronica Mars, where a young girl works in her father's detective agency.