Two Osgoods

In the aftermath of the previous Zygon attack on Earth, and The Doctor's actions to ensure the creation of a peace treaty (see "The Day of The Doctor"), there existed two versions of UNIT scientist Osgood: one human and the other a shapeshifting Zygon duplicate who do not divulge which is which since they considered themselves as both hybridized sisters and the personification of the treaty. Though the treaty allowed 20 million Zygons to remain on Earth, peacefully living out as disguised humans, The Doctor warned the Osgoods of the Nightmare Scenario should the treaty break, and left the two Osgoods with a mysterious container they called the Osgood Box. However, since that time, one of the Osgoods was killed by Missy (see "Dark Water/Death in Heaven"). Following her death the remaining Osgood left UNIT and disappeared.

In the present, the remaining Osgood is captured by Zygons, in the town of Truth or Consequences, New Mexico, United States of America, just after sending a warning to The Doctor that the Nightmare Scenario has occurred. Realising that a break in the ceasefire, between the humans and Zygons, has finally come The Doctor arrives on Earth and speaks with two known Zygon commanders, disguised as schoolgirls, but they are kidnapped by a Zygon splinter group before The Doctor can learn more. He attempts to call Clara as he travels to UNIT headquarters at the Tower of London. Kate Lethbridge-Stewart and her assistant Jac show him a video of Zygons killing the two commanders, followed by Osgood being forced to read a message from a small village in Turmezistan, declaring the Zygons' intent to go to war. The Doctor surmises this must be a small splinter group as the bulk of the Zygons want to live in peace. Kate reveals that she knows of Z67, a nerve gas that UNIT had developed that would only affect Zygons but that The Doctor had took away which could end this current situation, but The Doctor refuses to let them have it as he much prefers to find a peaceful solution.

Meanwhile, Clara is leaving for work and checks her mobile phone, to discover that The Doctor has left over 174 messages for her. She starts to listen to her voicemail, but finds a child crying on the stairs of her apartment complex. Clara recognises that the boy is Sandeep who lives in a nearby apartment. Learning that he cannot find his parents, Clara follows the child back to his apartment, finding it empty; however, the moment she turns around, the child's parents appear, saying nothing is wrong despite the boy's screams. Clara is concerned by this, but is next seen leaving without much of a care and soon meets The Doctor. Tacking command of the situation The Doctor sends Kate to Truth or Consequences, to learn more about that town, while he will travel to Turmezistan, via the airplane afforded him by being President of the World, to rescue Osgood. He instructs Clara and Jac to keep the homeland safe.

Osgood is Attacked

In Turmeszistan, The Doctor speaks to UNIT Commander Walsh, who explains how the Zygons have been able to take on the appearance of her soldiers' loved ones to prevent any attack on the village. With a bombing run planned, The Doctor joins Walsh and other troops as they converge on the chapel in town. The Zygons then appear as relatives and friends and, against Walsh's orders, lure all the soldiers into a chapel and kill them. The Doctor and Walsh enter through a back door, finding all the Zygons have escaped. Walsh gives The Doctor a few minutes before she will start the bombing run. The Doctor finds Osgood safe under the chapel, but they are cornered by a Zygon when they try to leave. However, the bombing creates debris that knocks the Zygon out. The Doctor and Osgood return to the airplane and fly back to England, during which The Doctor attempts to ply information from the Zygon. The Doctor believes that Missy killed the Zygon version of Osgood because the Zygons need the original person they're copying alive to maintain their disguise. However, Osgood reveals that she can be either one (but won't tell him which she is), since Zygons only use that method for spying on enemies; if they don't need to copy personalities, Zygons can keep someone's form without the original being alive.

In New Mexico, Kate finds the town of Truth or Consequences seemingly empty. While at the sheriff's office, she meets Sheriff Norlander who claims to be the last human alive after Zygons that lived among them turned and attacked them when their secret was discovered. While Kate is looking for more clues, Norlander is shown to be a Zygon, and prepares to kill Kate. Meanwhile at UNIT headquarters, Clara has Jac help her to get some things from her flat. While there, they see Sandeep's parents dragging a large bag into a lift. When the lift returns, they discover Zygon control units within it. They use the lift which take them to a series of tunnels under London where they discover many other lifts across the city connect to. They return with a troop of UNIT soldiers to explore the tunnels, and find thousands of Zygon pods which Clara announces must be where the Zygons are cloning themselves, and they must be destroyed. When one pod is revealed to contain Clara, Jac realises too late that Clara is a Zygon herself (having been switched when she first went to Sandeep's flat). The Zygon, that looks like Clara and calls itself Bonnie, states that the invasion has already occurred, with many of the humans in London already captured and replaced by Zygons. Jac and the troops are killed by Zygons when they attempt to escape. Bonnie then travels back to UNIT headquarters to obtain some equipment.

The Doctor

Aboard the airplane The Doctor interrogates the Zygon, learning that an all-out war is the only thing the Zygon splinter group want. He also learns that they have infiltrated numerous countries. Unbeknown to those aboard the airplane Bonnie has travelled to the coast and is watching the airplane approach. The Doctor calls Clara, only to get Bonnie, learning that he is talking to the leader of the splinter group. The Doctor immediately realises they are in danger when Bonnie tells The Doctor that his incoming airplane will never land. As it approaches Bonnie uses a shoulder-fired rocket launcher to fire a missile at the airplane. Saying good-bye to The Doctor she smiles when an explosion is heard.

Clara awakens in what seems to her apartment. However, she soon finds many inconsistencies with her home, such as the lack of windows and being unable to leave. Clara checks a magazine, finding it filled with gibberish; she's dreaming. She soon hears Bonnie's voice as the television in the living room turns on, showing exactly what she sees. Clara realising that she is able to control Bonnie's actions to a small degree, due to a telepathic connection between them, and seeing that The Doctor is in danger, makes Bonnie miss her first shot with the missile launcher. Clara though is unable to prevent Bonnie firing a second missile which strikes and destroys the airplane. Though Bonnie thinks The Doctor is dead, Clara pauses the image on her television, zooming in on a shadow falling away from the smoke. She relises that The Doctor is alive!

Having managed to parachute out of the plane, due to the delay created by Clara, The Doctor and Osgood land safely on a beach. Later, Bonnie finds a peaceful Zygon disguised as a human, and causes his body to revert to its Zygon nature in front of a shopping mall south of London. She uses Clara's mobile phone to record and upload the footage, starting a panic across news broadcasts. Meanwhile, Clara, through her telepathic connection, uses Bonnie to text The Doctor saying 'I'm Awake'. Osgood deduces from this that Bonnie didn't know that it was Clara who sent the text. The Doctor video calls Bonnie and, from the winks she exhibits, he recognises that Clara is able to give him small clues through Bonnie as to her pod's location. The Doctor and Osgood converge on the shopping mall where Bonnie's footage was taken, finding it empty save for the lone Zygon that Bonnie revealed. Fearing that he might have started a war due to revealing himself, he opts to kill himself instead of being discovered. Bonnie meanwhile goes to UNIT's headquarters to try to find information on the Osgood Box, but learns that The Doctor has given that information to Clara. In interrogating Clara via their telepathic connection, Bonnie learns the Osgood Box is in the Black Archives under the Tower of London. As The Doctor and Osgood prepare to look for Clara, they are met by the Zygon that has disguised itself as Kate Stewart, and two guards, who capture him and take him to join Bonnie. As they near the Black Archives, Kate reveals that she is not a Zygon, having shot and killed the one that cornered her in Truth or Consequences, New Mexico and falsified the report of her death to Bonnie. She then kills their Zygon guards. Her actions though annoys The Doctor who expresses his frustration at her violent methods.

Clara

Meanwhile, Bonnie has brought along Clara's pod so as to gain access to the Black Archives. Inside, Bonnie is furious to discover that there are two identical Osgood Boxes, only differing by colour. She calls The Doctor, who explains that one box has a button that contains a means that will remove the disguises of all 20 million Zygons on Earth, which would start a mass panic and likely lead to war, while the other box's button will release the Zygon-targeting nerve gas that would kill all of the Zygons. Bonnie demands Clara be removed from her pod to ask her directly of which is the proper box, but Clara does not know which box is which. By the time The Doctor, Osgood, and Kate arrive, Bonnie has found that either box's button reveals a second set of buttons labelled ‘Truth’ and ‘Consequences’ within both boxes.

When Bonnie prepares to press a button on the blue box, which would either expose the Zygons or make their human forms permanent, Kate prepares to do the same on the red box despite knowing she would either release the Zygon nerve gas or activate the nuclear warheads under London. The Doctor tries to talk both of them out this action - the Osgood Boxes have been a means to assure peace because of the consequences of the actions of either revealing all the Zygons or killing them all.

The Doctor explains that the Osgood Boxes are based on the Moment, a powerful weapon from the early days of Gallifrey, which, when he was known as the War Doctor, he considered using to end the senseless violence between the Daleks and the Time Lords that was destroying reality. However, with the help of his former incarnations, he thought better of it and was able to find a better solution. The pain from that still lives with him, allowing The Doctor to never again attempt something so horrible that it would make him discard his name. This revelation results in both Bonnie and Kate backing off with the former realising that the boxes are empty and were only a ploy to avoid a disaster. Kate points out that since they know this, this could cause the peace treaty to still break apart, but The Doctor tells them they've been in this situation fifteen times before, each time ending with The Doctor wiping their memories, as he initiates another memory wipe using the Black Archives defence system to achieve this again.

Realising that this time Bonnie has been swayed by The Doctor's words he spares Bonnie from the memory wipe, allowing her knowledge of the truth that this time will help resolve peace. Bonnie calls off the splinter Zygon group, telling her comrades that the revolution is over and that they are safe and so will live peacefully. Later, as The Doctor and Clara prepare to leave, The Doctor offers Osgood a chance to ride in the TARDIS, but she refuses saying that she needs to be around to prevent the Nightmare Scenario occurring again. Osgood then reveals her new duplicate - Bonnie, who has taken a new form after giving breaking her connection with Clara. Neither Osgood admits to which of them is human or Zygon, or if they are both Zygon. Both though agree to continue to protect the Osgood Box. After the TARDIS departs, both Osgoods decide to get an ice cream before heading back to UNIT.