Doctor Who: The Newbies Guide
Day of the Daleks
This is the first story in Season 9.
The Third Doctor has white hair, a large nose, and tends to dress as a society dandy. He has a love of technology, historical name-dropping, and vehicles. In The War Games the Doctor's people (the Time Lords) sentenced him to exile on Earth. In Spearhead from Space, he was appointed as scientific advisor to UNIT.
Brigadier Lethbridge-Stewart is the commanding officer of the United Nations Intelligence Taskforce (UNIT). He worked with the Second Doctor to defeat threats to Earth on two occasions (in The Web of Fear and The Invasion. In Spearhead from Space, he teamed up wiih the Third Doctor to prevent an invasion by the Nestene and the Autons. During that story he persuaded the Doctor to work as his scientific adviser.
Josephine "Jo" Grant is the Doctor's assistant at UNIT. She failed General Science A Level, but has had training in escapology, cryptology, and explosives.
Sergeant Benton is a UNIT officer. He has worked with the Doctor on numerous occasions.
Captain Mike Yates is an officer in UNIT. He worked with the Doctor on numerous occasions.
Recurring and Historical Characters
The Daleks are a race of evil mutants encased in powerful cyborg bodies whose shape is reminiscent of pepperpots. The Doctor has fought them many times, first encountering them on their home planet of Skaro in The Daleks. In The Dalek Invasion of Earth, they had conquered 22nd Century Earth. In The Chase, The Daleks Masterplan, and The Evil of the Daleks show the Daleks having access to time travel technology. The Doctor considers the Daleks his greatest enemy, and they are a serious threat to anyone they encounter.
The United Nations Intelligence Taskforce (UNIT) is an organisation devoted to protecting Earth from extra-terrestrial threats, In The Invasion, the second Doctor teamed up with them to prevent an invasion by the Cybermen. In Spearhead from Space, the Doctor became their scientific advisor.
Whilst the story refers back to a couple of previous Dalek stories, you only really need to know that they are an old enemy of the Doctor.