The Doctors trial is over and the Time Lords have done exactly as they said they would do. He has regenerated and suffering from memory loss, primarily in regards to the Tardis and it's functions. They materialize the Tardis on Earth and he stumbles out, traumatized by the regeneration. The Doctor is exhausted and somewhat erratic, a trademark for future regeneration stories.
Does anyone know the golden rule when finding a flashing meteorite from space? ALWAYS! Wait, no. NEVER touch it! But some people are not so smart. The Time Lords have seen fit to deposit the Doctor on Earth at the start of an Nestene invasion. The Nestene is able to control plastic such as dolls or mannequins, and a nearby plastic facility has begun to produce mannequins en masse.
Investigating the strange meteoroid storms is the Brigadier from UNIT. He has sent for Liz Shaw who is an expert on Meteors and the like. But when he hears a man is found in Oxley Woods along with a police box, he is immediately aware the Doctor may be available to help. Because of the regeneration, he doesn't recognize the Doctor, but the Doctor recognizes him. However the Doctor is still tired and exhausted, so he's left to rest in the hospital.
The Nestene has already detected the Doctor may be a threat and attempts to kidnap him from the hospital. The Doctor escapes however, only to be shot by a UNIT soldier. He's only grazed though, and quickly recovers. The action seems to have fueled the Doctor and he's ready to go. He procures a set of clothes as well as a car and heads for UNIT and his Tardis. But the Tardis is locked and the Brigadier has the key.
Reluctantly the Doctor helps, but tricks Liz into acquiring the key to the Tardis. She doesn't believe the Tardis is a time machine and sees no harm in giving it to him. The urge to run overtakes the Doctor and he attempts to take off. But the dematerialization code has also been changed, he is marooned. He formally agrees to help as long as he is able to work on his Tardis and have Liz Shaw's help.
With the combined resources of UNIT and equipment from the Tardis, the Doctor is able to create a device capable of stopping the Autons. Problem is, he has to get close to the Nestene to affectively use it. With UNIT's help, he makes his way to the Nestene, but the device fails to work. Fortunately Liz is able to quickly determine what's wrong. The Nestene has been defeated.... for now.
WHO: Liz Shaw
PLANET OF ORIGIN: Earth, circa 1970
REASON FOR JOINING: Enlisted by the Brigadier, she remains to help the Doctor as his assistant.
NEXT: Operation: Mole-Bore