In 1943, two American soldiers unload bodies from a truck as they prepare to burn them. After grabbing gas cans, they spot the Nogitsune. Shooting it does nothing and it kills one of the soldiers. It chases the other down and rips his head off after telling him a riddle.
Mr. Yukimura notices a fly in his classroom. Stiles enters soon after and wants to know where Mrs. Yukimura keeps the blades that represent her tails. Yukimura feigns innocence but Stiles promises he will talk. He sends a fly down Yukimura's throat.
Scott and Kira look at an old photograph that they suspect is Kira's grandmother. Kira receives a text that her father is in danger. They rush to the school where they find Kira's parents. Mrs. Yukimura feeds her husband something that causes him to spit up a black mess. She explains that she has kept the last knife on her since Stiles disappeared. Kira shows her mother the photo who states that it's actually her. She has a flashback to 1943 and reveals that she's almost 900 years old. Kira hands over her katana and Mrs. Yukimura reveals the sword shattered the last time it was used, in 1943. She tells them about an internment camp at Oak Creek that was covered up. Kira asks where the Nogitsune came from and Mrs. Yukimura says it came from her.
At Oak Creek in 1943, a young Mrs. Yukimura shares the items she stole from the American soldiers. Soldiers enter the building they are staying in. They warn that there will be an inspection tomorrow.
Kira wants to know everything before helping her mother. Mrs. Yukimura doesn't think foxes and wolves get along but Mr. Yukimura is happy to have allies in the time of war.
As Argent and Derek prepare to leave the prison, Parrish gives Argent a hard time about one of his weapons. Stilinski walks up and says he's responsible for getting them out of jail. He tells Parrish he'll take care of it. Stilinski shows Argent and Derek brain scans from his wife and Stiles. They are exactly the same and says that should be impossible. The sheriff asks both of them to help stop Stiles because they are experienced in this type of business. Stilinski wants Stiles trapped and hands Argent his weapon back.
In 1943, Mrs. Yukimura meets with her American soldier boyfriend. He asks her to ease up on the things she's stealing from the army. He warns that everyone will get punished for the thefts. Kira wants to hear how to stop Stiles and Scott thinks Mrs. Yukimura is stalling. She says he won't want her to call off the Oni once he hears the rest of the story.
At the Argent house, Derek explains that Stiles is trying to get them to repeat the same pattern. Allison isn't sure what they should do because everyone's trying to out fox the fox. They all split up to try to find Stiles.
Mrs. Yukimura continues her tale about the American she was seeing in 1943. He was set to be deployed to North Africa in a few weeks. They overhear two soldiers talking to the camp doctor and exchanging money. In the present, Mrs. Yukimura reveals one of her talents is healing. Many of those in the internment camps got pneumonia and the soldier said there was no more medication. The doctor was using a soldier to sell the medicine on the black market. Mrs. Yukimura feels she spoke too soon and incited a riot. The Japanese surround the doctor's car and say they want him. She tried to stop them but there were too many who were angry about the sick. One soldier punches an elderly woman to the ground. The woman's eyes glow and it was then Mrs. Yukimura realized she was a werewolf who was always trying to stay calm. She grabs a molotov cocktail from one of the men and throws it at Mrs. Yukimura's boyfriend, who goes up in flames.
While Allison and Stilinski are in an elevator at the hospital, she starts to freak out. She admits she acts like she knows what she's doing but she doesn't. She feels very unsure and afraid but Stilinski hugs her. He says she sounds just like a cop and assures her she'll be fine. He receives a text that shows someone has broken into his house. He opens the video feed and it shows Stiles in his room waving at the camera.
In 943, the soldiers open fire on the Japanese rioters and almost kill Mrs. Yukimura. She tells Kira that she was barely alive because of how many bullets had hit her. She was actually mistaken as dead because her pulse was undetectable. She was still better off than her boyfriend, who received major burns to his body before eventually dying. The doctor had also sold the morphine. Two soldiers were given the task of disposing of all the bodies so that the incident could be covered up. She wound up next to her boyfriend's body in the truck. She wanted those responsible to pay and knew she was running out of time. Her body was too weak to move and she would have been burned with the other bodies. She called out to her ancestors for a powerful Nogitsune to take control of her body to use it as a weapon. The trickster demon came but instead it possessed her boyfriend's body. Scott asks what the Nogitsune did after it got away from her. She explains it brought more pain than can be imagined. She later returned to Eichen House to find everyone there dead. She knew she had to stop him herself and fought him with her katana. The older Japanese werewolf helped her to defeat the Nogitsune. A fly comes out of the body and Mrs. Yukimura grabs it.
Mrs. Yukimura tells Kira that she needs a lightning bolt to put the katana back together and Kira is the only one who can do that. Kira melds the sword back together
Everyone regroups at Stiles' room. A game of chess is laid out with sticky notes, containing the names of everyone, on the pieces. Argent thinks it's a threat from the Nogitsune but others think it's a message from Stiles. It wants to meet at the loft and Stilinski thinks they need to out trick it.
Mrs. Yukimura hands her katana to Kira and says it's now hers. She warns she will need it to stop Stiles if the Oni can't. The only way to save Stiles is to kill him but Scott doesn't want to believe that. He receives a text from Alison to meet at the loft. Mrs. Yukimura buried the jar containing the fly, deep in the roots of the Nemeton. Allison, Stiles and Scott's sacrifice brought its power back. They let the demon back out and solidified their part in this.
Stilinski enters the loft and finds Stiles standing inside alone.