In Northern Italy in 49BC, shortly before Julius Caesar will cross the Rubicon, the Doctor and Ace walk through a Roman camp, the Doctor worried about mention of a mysterious advisor to Caesar that he's recently read about. Arriving at the general's tent, the advisor, the Master allows the two entrance.
Entering, the two find Caesar lying on a bed, the Master having already poisoned him. As the Doctor despairs at his once friend's villainy, the Master reveals that he intends to cross the Rubicon and take control of the Roman Empire, using his Time Lord knowledge to turn it into an interstellar state.
At this moment, Caesar rises having been advised by the Doctor not to take the poison though the Master attempts to flee, he is quickly taken prisoner while Caesar gives the Doctor his thanks. As the Doctor and Ace leave to send the past version of Caesar advice, Ace wonders what will become of the Master, with the Doctor quite confident that he'll be back.
And of course, the Master did return. And would eventually rekindle their friendship with the Doctor. Though by that point, the Master would be a woman.
- The Doctor refers to Julius Caesar's crossing of the Rubicon as a fixed point in time.
- The Doctor assumes the Master will flee in his own TARDIS.
- This story is a rare example of using the dating system of BCE (Before Common Era) over BC (Before Christ).
- The Doctor borrowed a book on Roman history from the Lux Foundation Library. (TV: Silence in the Library, Forest of the Dead)
- Ace recognises the Master. (TV: Survival)
- The Doctor uses the alias "Septimus Doctus", despite the Master was expecting him to use "Theta Sigma". (TV: The Armageddon Factor, The Happiness Patrol) The Doctor likewise wonders why the Master doesn't use "Magister", which the Master views as "old hat". (TV: The Dæmons)