A slimy gossip columnist is killed and it's up to Simon to find the true murderer from the list of subjects.
Leela is concerned by the Doctor's strange behaviour when, after a secret meeting with aliens, he returns to Gallifrey and abruptly stakes his claim on the Time Lord presidency.
Stor, the Sontaran leader, finally gains access to the TARDIS in search of the Great Key of Rassilon and a dangerous game of hide and seek begins inside the Doctor's ship.
A 15th century prayer volume disappears from a sealed casket inside the locked safe belonging to an Oxford Don. An illusionist is called in to demonstrate how the book can disappear from a locked safe, when the supernatural is suspected.
Authorities become alarmed when they realize parts of an atomic bomb are found among the baggage from a crashed airliner. The Invisible man is tasked with finding out the source of the parts.