Gerta is a 12-year-old girl living in East Germany whose family is suddenly partitioned by the Berlin Wall. Initially ignorant of the political landscape, her separation from her father and brother sparks a growing rebellious streak. She is observant and determined, struggling to suppress her irritation during state indoctrination at school and the Pioneer Club.

Fritz is Gerta's older brother and closest confidant in their restricted East German environment. He harbors a deep resentment for the regime and craves Western amenities like Beatles albums and Coca-Cola. Approaching his eighteenth birthday, he faces the looming threat of mandatory military conscription into the National People's Army.

Aldous is Gerta's father, a man with a history of criticizing the government and participating in dissident activities. He is separated from his wife and two of his children when he travels to West Berlin for employment opportunities. Though physically absent for much of Gerta's daily life, his quiet resistance and secret messages provide a source of hope for his family.

Gerta's mother is a traumatized survivor of World War II who desperately desires safety, stability, and enough food for her children. She wants nothing to do with protests or dissidence, insisting that her family learn to accept their new reality and comply with the East German state. Her primary goal is to keep her children out of danger, often putting her at odds with their rebellious instincts.

Anna is Gerta's shy and compliant best friend. She prefers to play it safe and conform to the expectations of the East German government, focusing on mundane concerns like school and weather. Her friendship with Gerta becomes strained by the dangerous political realities surrounding their respective families.

Herr Krause is the Lowe family's elderly next-door neighbor. He survived two world wars but remains an active dissident against the East German government. Despite the extreme danger, he operates a secret printing press from his home to distribute anti-government messages, earning him the suspicion of the Stasi.

Dominic is Gerta's other brother, who happens to be traveling in West Berlin with their father when the wall is erected. Because of this poorly timed trip, he is cut off from his mother, Gerta, and Fritz, becoming a resident of the West while his siblings remain trapped in the East.

Officer Muller is a border guard (Grenzer) assigned to watch the Death Strip between East and West Berlin. He enforces the state's harsh rules, carrying a weapon and intimidating citizens who look too closely at the wall. However, his interactions with Gerta suggest he has a family of his own to consider.

Peter is Anna's older brother. Unwilling to live under the restrictive rules of East Germany and unable to choose his own future, he makes a desperate and dangerous attempt to cross the wall into the West.

Viktor is a former childhood friend of Fritz who has since joined the Stasi. Once considered a "good guy," he now uses his position of authority to enforce the will of the state, intimidating his former friends and neighbors while enjoying the perks of his powerful job.

Frau Eberhart is a nosy neighborhood busybody who constantly monitors the activities of those around her. In East Germany, her habit of prying is incredibly dangerous, as citizens know informants are well-paid by the Stasi for reporting suspicious behavior.

Claudia is Fritz's girlfriend. She represents a normal adolescent milestone for Fritz, but their relationship is complicated by the state's surveillance. Her family is loyal to East Germany, making her continued association with the dissident Lowe family politically risky.

Oma Gertrude is Gerta's grandmother, who lives in the countryside outside of Berlin. She requires temporary care after an injury, creating an opportunity for Gerta and Fritz to spend time alone in the city without their mother's strict oversight.