Doctor Who: The Newbies Guide
Arc of Infinity
This is the first story in Season 20.
The Fifth Doctor is physically younger than his previous incarnations. He wears Edwardian cricketing clothes with a stick of celery on the lapel. He is less eccentric than his previous incarnations. In Earthshock he was unable to save his companion Adric from dying.
Nyssa of Traken is the daughter of Tremas of Traken. In The Keeper of Traken she helped the Doctor and Adric to defeat the Melkur, a living statue that threatened their planet. The Melkur was actually the Master's TARDIS, and at the end of that story the Master took over her father's body. In Logopolis, the Master destroyed a large portion of the universe, including Traken.
Tegan Jovanka is an Australian air stewardess who accidentally stumbled into the TARDIS in Logopolis. She has a tendency to moan. In Time-Flight she was left behind in her native time.
Recurring and Historical Characters
The Time Lords are the Doctor's own people. . In The War Games they exiled the Doctor to Earth, allowing him to leave a few times in order to perform missions for them. In The Three Doctors they lifted his exile as thanks for helping deal with a crisis caused by Omega. Since then they have occasionally asked him to perform missions for them. In The Deadly Assassin, the Doctor returned home and was involved in uncovering a plot by the Master which involved assassinating the Time Lord President. In The Invasion of Time the Doctor briefly became their President.
Omega is one of the legendary founders of Time Lord society. In The Three Doctors he was discovered to be imprisoned a the black hole that he had created. The second and third Doctor (with advice from the first) prevented his attempt to escape.
The Doctor's previous defeat of Omega was seen in The Three Doctors.