The Ministry is called to investigate when archaeologists find a cell phone belonging to a missing 21st century corrupt executive in a room that was sealed off in 1520.
The company Walcott works for is named Darrow Ltd. as an homage to the novel "The Gates of Anubis".
The time door to 1520 Salamanca is inside a confessional booth in an abandoned church. Confessionals were introduced during the Council of Trent (1545-1563).