Message #78251

[Jas765]

5127

Yeah, I know.

Well...

The episode begins with the Doctor and his companion Donna Noble strolling through a market place on the Chino-planet of Shan Shen. Donna is persuaded by a fortune teller to examine her past: specifically, the first event that led to her encounter with the Doctor. Donna recalls an argument with her mother Sylvia at a road junction: Donna wishes to turn left to become a temporary employee at the security firm H. C. Clements; her mother wishes for her to turn right to apply for a secretarial job at a local photocopying business. The fortune teller gives her another chance and persuades her to turn right; as she does, a large beetle crawls onto her back.
The narrative focuses on an alternate history where Donna never met the Doctor and recalls several previous episodes: the Doctor dies during the events of "The Runaway Bride", leading to the deaths of his companions during the events of "Smith and Jones" and "The Poison Sky," the nuclear destruction of London during "Voyage of the Damned" and resulting dystopia, and deaths of millions in the United States during "Partners in Crime". Throughout the episode, several characters, most notably Rose Tyler, take an interest in the invisible beetle on her back.
After the events of "The Poison Sky", Rose tells Donna of their comparable roles in the Doctor's life and explains that Donna is instrumental to saving the universe. When Donna's grandfather Wilfred Mott sees the stars go out, Donna acquiesces to Rose's request: she must travel back in time and ensure her past self turns left at the junction. With the help of a UNIT detachment who have been analyzing the crippled TARDIS, Donna is shown the creature on her back and told how to intervene once in the past. After Donna materialises in Sutton Court, Chiswick, she realises she cannot directly influence herself at the junction; instead, she causes a traffic jam by stepping in front of a haulage truck. As she dies, Rose whispers two words for her to relay to the Doctor: "Bad Wolf."
The episode's final scene takes place on Shan Shen, where Donna's actions cause the beetle to fall off her back and the fortune teller to flee in fear. The Doctor appears and inspects the beetle: he says that it is part of the "Trickster's brigade", a menagerie of monsters that change timelines in small ways. He comments that Donna's actions inadvertently created a parallel universe and compliments her unusualness; she replies by mentioning Rose and repeating her final words. A panicking Doctor exits the fortune teller's room and sees all text rendered as "Bad Wolf". He enters the TARDIS, and after hearing its Cloister Bell ringing, realises the end of the universe is imminent.

Just so you know, "Bad Wolf" was a message spread throughout time and space by Rose Tyler after infusing herself with the power of the time vortex at the heart of the TARDIS.

All taken from wikipedia.