Having lost his job in a traveling circus, Jewish American performer Abel Rosenberg, his brother and trapeze partner, Max, and Max’s ex-wife Manuela, struggle to survive in 1923 Berlin, Germany. One night in early November, Abel returns to his boardinghouse room and finds that Max has shot himself in the head. At police headquarters, Abel informs Police Inspector Bauer that he and his brother were let go from the circus because Max hurt his wrist and could no longer perform. Bauer asks if Max was depressed, but Abel does not know. When Bauer asks if he is Jewish, Abel does not answer, suspecting that Bauer is anti-Semitic. At the cabaret where Manuela works, Abel delivers the news of Max’s suicide, but Manuela is not surprised. They read Max’s suicide note, which is mostly illegible but contains the cryptic phrase, “There’s poisoning going on.” Backstage, Abel runs into Hans Vergerus, a childhood acquaintance. Leaving the cabaret, Abel sees a group of thugs beating a man, and, sensing danger, runs to a bar. Later, Manuela finds Abel drunk outside her building and takes him in. The next morning, she offers to take care of him for a while. After she leaves, Abel steals cash from Manuela’s dresser and returns to his boardinghouse to pick up his things. However, Inspector Bauer stops him on the way and escorts him to the morgue, where Abel is asked to identify several corpses. The bodies, all found dead under mysterious circumstances, belong to Max’s fiancée, a woman Abel recognizes from the boardinghouse, and a boy who worked with Manuela at the cabaret. After admitting to being an alcoholic, Abel deduces that he is a murder suspect and worries that Bauer has targeted him because he is Jewish. Abel escapes Bauer’s office but gets trapped in the gated corridors of the building before being knocked out by guards and jailed. While in custody, Abel receives a visit from Manuela, who has become sick. She reports that her savings were stolen from her apartment, but Abel does not admit guilt. Once released from prison by the sympathetic Bauer, Abel finds Manuela with Vergerus at the cabaret. Abel becomes suspicious that the two are in a relationship, and Manuela later confirms it, also revealing that she has been working as a prostitute during the daytime. Abel secretly follows Manuela to a church where she confesses her guilt over Max’s death to an American priest. Unable to grant assurance that God can hear their prayers, the priest prays for Manuela and grants his personal forgiveness. Continuing to follow Manuela, Abel discovers that Vergerus has given her a new apartment. Initially angry and opposed to living there, Abel finds that he cannot abandon her because they have developed an emotional connection. That night at the cabaret, Abel listens to the woes of the cabaret owner. Suddenly, anti-Semitic soldiers raid the theater, smashing the cabaret owner’s face and setting the establishment on fire. The next morning, Abel goes to work at the archives of the St. Anna Clinic, a position offered him by Vergerus. He is introduced to the two archivists, Dr. Soltermann and Dr. Silbermann, who show him to his workroom deep within the labyrinthine complex. During a break, Abel visits the clinic’s laundry site, where an increasingly ailing Manuela has gotten a new job, also thanks to Vergerus. That evening, a fearful Dr. Silbermann shows Abel a collection of secret files containing reports on Vergerus’s medical research involving experimentation on human subjects. At Manuela’s new apartment, Abel complains of an incessant engine-like noise, and Manuela loses her patience, ordering him to leave. When she softens and tries to kiss him, Abel stops her and refuses to make love. He flees to a brothel where he spends the night with two prostitutes. In the morning, Abel returns to the apartment to find that Manuela has died of her illness. When a man behind a one-way mirror snaps a photograph, Abel detects the flash and realizes the entire apartment is being surveilled by movie cameras behind two-way mirrors. Running downstairs, Abel finds a complex of abandoned medical facilities, the original site of Vergerus’s human experimentations. When ambushed, Abel holds his attacker’s head under a descending elevator and kills him. Returning to the St. Anna Clinic, Abel takes Dr. Soltermann’s keys and heads into a vault where Vergerus projects films of his experiments. As Abel views the films, Vergerus explains what is happening onscreen. In one, a young man’s descent into emotional terror is brought on by the injection of a drug. Vergerus says the subject committed suicide after he was released from the clinic, then explains that Max’s depression and suicide were the result of his participation in the same experiment. Max had been one of Vegerus’s assistants, and though he was warned against trying the drug himself, Max’s fascination led him to take it. Vergerus describes his experiments as the beginning of a social program based on the ideas of eugenics. Although believing that the conditions are not yet right for the implementation of a new society and that the Nazi party leader, Adolf Hitler, is too dimwitted to lead a revolution, Vergerus is convinced that a new Germany will emerge in ten years when angry youth converge with a strong leader. Vergerus predicts that Germans will effectively exterminate inferior human beings, and the records of his experiments will serve as inspiration to future scientists. The police arrive and attempt to break down the vault door, prompting Vergerus to commit suicide by swallowing a cyanide capsule. Abel wakes up from a drug-induced sleep two days later at police headquarters. Inspector Bauer happily informs him that Hitler’s attempted putsch in Munich failed and laughs that the Nazi leader underestimated German democracy. Bauer says he found Abel a new job at a traveling circus. However, as a police escort transports him to the train station, Abel escapes and is never heard from again.