Turn Left was the eleventh episode of the fourth series of Doctor Who. It was the first Doctor-lite episode to focus on the main companion without the Doctor, and marked the first major reappearance of Rose Tyler. It also showed an alternate timeline for the episodes following Donna’s original meeting with the Tenth Doctor in The Runaway Bride. In that alternate timeline, many of the Doctor’s companions and friends would have died. Much of series 3 and 4’s events set on present day Earth would still occur, but would have cost more lives without the Doctor’s intervention. The Master would not have been present in his Harold Saxon persona as the Doctor would not have been alive to go to the year 100 trillion to allow him to escape the end of the universe.
The Tenth Doctor and Donna are in a busting market place on an alien world, mixing with the locals. Donna wanders away from the Doctor to explore as he chats away with a merchant. A mysterious fortune teller asks if she wants her future told, but Donna declines. The fortune teller then says the reading is free for those with red hair. Donna smiles and relents. As the fortune teller asks abaout Donna’s past, she sees there is a man in her life that changed everything. Donna experiences a flashback, but the fortune teller dismisses it. The teller asks Donna what event led to her meeting with the Doctor and Donna says it was in June 2007.
At that time, Donna and her mother were in a car at a T-junction, arguing about her future. Sylvia tried to persuade Donna to turn right and ask businessman Jival Chowdry for a job; but Donna turned left to go to her planned temp job at H.C. Clements. After experiencing another flashback, Donna is now panicking, but the fortune teller asks her what would have happened if she never met the Doctor as something crawls onto Donna’s back. Scared, Donna falls under the fortune teller’s influence and, in the past, she gives in to her mother’s nagging and turns right, altering the course of her life as well as the future of all existence.
It is Christmas Eve 2007, and Donna is at a Christmas party with the rest of the staff from her workplace. She has just been promoted to Jival Chowdry’s personal assistant. Suddenly the Racnoss Webstar attacks London, and is destroyed by the army at a terrible cost. During the chaos,Alice stares at Donna’s back, looking terrified. When Donna acts astonished that Alice’s attention is focused on her despite the ongoing chaos, Alice, terrified, says that there is something on Donna’s back. After this, Donna runs to the Webstar’s general location. There she finds an ambulance. Near the ambulance and a group of UNIT vehicles, Donna overhears a UNIT officer talking into a radio about someone who drowned beneath the Thames. As the persons body is loaded into an ambulance, a hand falls out of the stretcher, dropping a small metal stick. As Donna walks away, Rose Tyler comes running down the street and asks for information about the body that has just been loaded into the ambulance. She is stunned to hear that it was the Doctor, despite Donna’s assurances that it could have been any doctor. Rose vanishes moments later.
In April 2008, Donna is fired from her job. Chowdry tries to tell her that he has to lay people off because half of his contracts are on the other side of the river. Even though it has been several months since the Racnoss attack, the Thames is still closed off. Meanwhile, the Royal Hope Hospital is mysteriously transported to the Moon. When it returns, there is only one survivor: medical student Oliver Morgenstern, who relates the terrible events. As in the original timeline, the hospital had been moved by the Judoon and infiltrated by a Plasmavore. Sarah Jane Smith (at the hospital with her son, Luke Smith and his friends, Maria Jackson and Clyde Langer) filled the Doctor’s role, and stopped the MRI from irradiating the Earth — but, without the Doctor, the humans couldn’t find a way back to Earth, and all suffocated. Oliver Morgenstern tells reporters he only survived when fellow medical student Martha Jones gave him the last of her oxygen.
As Donna digests the terrible news, Rose tells Donna that she should go to the country for Christmas in 2008.
Donna takes the woman’s advice, and treats her mum and grandfather to a Christmas holiday in the English countryside. On Christmas morning 2008, they watch the telly in disbelief as a replica of the Titanic falls on Buckingham Palace. The three run outside and watch, horrified, as a mushroom cloud rises above London. Donna turns to see the housemaid, who resembles the mysterious fortune teller, pointing angrily at her, presumably for escaping her intended death.
Now refugees since all of southern England has been flooded with radiation, the Nobles are forced to move to Leeds. France has closed its borders. They are allocated a house that is shared with two other families.
In 2009, the United States pledges to help Britain with monetary relief but must abandon the plan when their own crisis strikes: sixty million Americans are turned into Adipose. Since London no longer exists, Adipose Industries had targeted the USA.
Some time later, Donna finds soldiers firing at cars when the Sontarans activate the ATMOS devices, covering the Earth with a poisonous fog. A soldier notices something on Donna’s back and holds her at gunpoint, but she is released when nothing is there. That night, Donna meets Rose for a third time. Rose explains that the Torchwood team, aboard the Sontaran ship, are trying to stop the catastrophe. Suddenly, the sky is cleared by an atmospheric converter. Gwen Cooper and Ianto Jones have given their lives to achieve this, and Captain Jack Harkness has been stranded on the Sontaran homeworld.
Rose refuses to tell Donna her name. She only says that she has “crossed reality” (coming from the parallel world on which she was trapped), and tries to explain that Donna had saved the Doctor’s life in an alternate timeline, though Donna insists that she had never met him. Rose warns Donna the coming “darkness” threatens every single universe. Donna tries to walk away, but Rose tells her that she will have to go with her when she is ready and that she has three weeks to decide. She warns Donna that when she comes with her, Donna will die. Then she disappears.
Three weeks later, the genial Italian family in Donna’s house is evicted as England is now “only for the English”. Since the oceans are closed off, they must be taken to a “labor camp”. “That’s what they called them the last time,” Wilfred says horrified, “it is happening again!”, alluding to the concentration camps of World War II. Later at night, Donna and Wilf talk about recent events while looking through his telescope. He notices that the constellation of Orion has gone, though there are no clouds. As the stars disappear from the sky, Donna finds Rose, and tells her that she is ready.
Rose takes Donna to a UNIT base and shows her the TARDIS — salvaged from beneath the River Thames — which is dying after the Doctor’s death. Rose asks Donna if she wants to see the creature on her back. They step into a circle of mirrors and lights, with pieces of technology which seem to be scavenged from the TARDIS. Rose switches on a light which reveals what is on Donna’s back: a “Time Beetle”. Donna is horrified and begs Rose to get it off her. However, Rose explains that it “feeds off time by changing time” and that she thinks the beetle is in a state of flux, although when Donna asks what that means, Rose says she doesn’t know, but that it’s something the Doctor would say. She also says the beetle cannot be removed; when Donna becomes angry that Rose said she was special but Donna thinks it wasn’t her, but the beetle, Rose says that actually they’re getting separate readings from Donna that make it seem like reality is bending around her. Donna asks, “What can I do to get rid of it?” to which Rose replies, “You’re gonna travel in time.”
They prepare Donna, and take her back to the circle of mirrors and technology, with cables running into the TARDIS. At first Donna thinks she is going to see the creature again and protests, but Rose informs her the mirrors are “incidental”, and that they “bounce Chronon energy at the center, which we control and decide the destination.” Donna realizes that this is the time machine they will be using. When Donna asks, “How d’you know it’s gonna work?” Rose replies “Hmm? Oh, yeah we don’t… We’re just guessing”.
Donna says “I’m ready, ‘cuz I understand now, you said I was gonna die but, you mean, this whole world is gonna blink out of existence, but that’s not dying, because a better world takes its place — the Doctor’s world. And I’m still alive. That’s right?” Rose remains silent. “That’s right, isn’t it?” Donna tries to get confirmation of her belief, but Rose only replies sadly, “I’m sorry.” Before Donna can learn what will happen, she is sent back in time.
Donna lands in June 2007, elated that the time travel worked, but quickly realizes that she is a half a mile away from her past self and has only got four minutes to prevent her past self from turning right. She tries to run to herself, but knows that she will not make it in time. Donna understands what the woman meant about her death, and she sees a haulage truck coming along that has just passed by her past self. She steps in front of the truck, which screeches to a stop.
Before Donna dies, Rose appears and whispers something into her ear to tell the Doctor. At the intersection, Donna’s past self decides that instead of sitting in backed up traffic, she will turn left.
As the original timeline reasserts itself, Donna regains consciousness in the fortune teller’s stall on Shan Shen. The baffled and terrified fortune teller flees, screaming, “You were so strong. What are you!? What will you be?!” The Doctor, who has been blissfully unaware of all that’s happened, enters and an emotionally spent Donna collapses into his arms. When he asks why, she simply replies, “I don’t know!” and proceeds to hug him again.
Upon examining the beetle, the Doctor tells Donna that it is part of the Trickster’s Brigade and that normally it affects one person and the universe compensates (as happened to Sarah Jane Smith), but in Donna’s case, it created a parallel universe. The Doctor muses on all of the coincidences surrounding Donna: the fact that she had two parallel worlds that formed around her (this one and the one in the CAL computer) and that he’s met her and her grandfather twice. “In the whole wide universe, I met you again,” he notes.
The Doctor concludes that they seem to be somehow linked. Donna tells the Doctor she is nothing special, but he counters saying that she’s “brilliant”. Hearing that triggers Donna’s memories of the parallel world and she mentions Rose to the Doctor. When asked if she remembered Rose’s name, Donna said she was never told it, but she does remember the two words Rose whispered into her ear: “Bad Wolf”. Terrified, the Doctor runs out into the market square to see the words “Bad Wolf” everywhere: on posters pasted onto the walls, on the ceremonial flags hanging over the market, even on the TARDIS itself. Inside the TARDIS, the control room is glowing red and the Cloister Bell is ringing. When Donna asks what’s going on, the Doctor replies, looking horror stricken, “It’s the end of the universe.”