In the opening scene of "Unfamiliar," a mysterious man is seated on a public bench, his movements focused and deliberate. He uses a knife to remove a small device from beneath his skin and then, without hesitation, fires a bullet into his leg. The scene shifts to a cozy house where a young girl named Nina is celebrating her 16th birthday with her parents, Simon and Meret Schäfer. As they prepare for the festivities, Simon receives a call from an unknown number. The voice on the other end of the line is that of the man from the earlier scene, who informs Simon that he has been injured and needs help. He offers a significant sum of money for his services.
Simon and Meret rush to the man's location and bring him to a safe house, where they tend to his wounds while keeping a wary eye on his identity. Shortly thereafter, Simon returns to Nina's side, while Meret remains at the safe house.
The scene then shifts to the German Foreign Intelligence Service headquarters in Berlin, known as the BND. The team lead, Ben, announces that they are investigating Josef Kaleeve, a high-ranking Russian official whose wife, Vera, is about to become the Russian ambassador in Berlin. Josef's past is rife with shady deals, and the German government is hesitant to approve Vera's appointment. They need to uncover why Josef has entered the country before Vera. The previous head of the BND, Gregor Klein, arrives at the office at Ben's request but claims to have no useful information about Josef.
Back at the safe house, the injured man tells Meret that he used to work for a security company. He explains that he stole something from them and was pursued by them, leading to the gunshot wound. Simon goes home and tells Nina that they had to attend to a friend whose house was broken into. He assures her that Meret is safe but advises her to stay home for her birthday.
While Meret is away, the injured man steals her fingerprints from a glass of water. Meret later discovers this on her security cameras and calls Simon, telling him that the man assumed they were brother and sister. The only time they pretended to be brother and sister was during a mission in Belarus.
A flashback takes us 16 years ago in Belarus. Simon and Meret are driving when Simon discovers a fake passport for a woman named Katya hidden in the car. They have been sent by Gregor Klein on a mission to help Katya escape. They reach the safe house and realize it's been compromised. Inside, they find Gregor bleeding from a gunshot wound and Katya unconscious from poison.
Currently, Gregor informs Julika that Josef will not be performing his own dirty work here and advises her to find his middleman. The next scene introduces Jonas, a man who warmly welcomes Josef Kaleev and they get into a car together. It turns out that they are the ones who sent the agents to the Schäfers. They don't know the Schäfers' identity, but Jonas believes that these agents must be the ones Josef is looking for.
At the safe house, Meret informs the injured man that she is going out but spies on him from a different location. The man sneaks into the security room and uses the computer to contact Jonas. He sends Jonas a picture of Meret's fingerprint, and that's when Meret fills the room with a gas that knocks him out.
Jonas receives the picture from his agent and scans the fingerprint, which identifies Meret. The database states that she and her husband were killed in action. Josef recognizes them as the people he is after and orders Jonas to execute both of them and Gregor as well. Jonas seems to hesitate—did he recognize Meret?—and then sends the order.
Gregor is at a bar with his friends when he realizes something is off. He goes to the toilet and a woman follows, gun in hand. But she doesn't find him. Gregor is on the other side of a one-way mirror, watching her.
Elsewhere, Simon is on his way to pick up Nina when a man bumps into him. He suddenly gets dizzy and falls down. Meanwhile, the female assassin tells Jonas that she lost Gregor. Josef isn't happy with this development and tells Jonas he's fired.
Meret returns to the safe house and sees the kill order sent by Jonas on her computer. She ties the agent to a chair and starts questioning him. He gets loose and they engage in a fight. In the end, she manages to take him down. She then gets a call from the hospital and rushes to see Simon.
Based on what Gregor mentioned, Julika starts looking into the Belarus case from 16 years ago. She looks for the file but finds it filled with blank pages. At the same time, Josef leaves a voicemail for his mole in the BND. It reaches a phone which is taped to the top of an elevator in the office.
At the hospital, Simon tells Meret that he passed out due to high blood pressure and it's nothing to worry about. They head to the party where Nina is DJ-ing and then go home together. The next day, they meet Gregor, who tells them that Josef is trying to "clean up" before his wife becomes the ambassador. He advises them to kill Josef before he kills them.
A flashback shows that Katya was still alive when the Schäfers found her. They manage to save her baby through a cesarean delivery. Currently, Meret receives a phone call and realizes it's Katya on the other end. She's alive! And in Berlin, in trouble with the police. Meret realizes that Simon lied to her.
