In 1945, Otto Frank returns to Amsterdam after the conclusion of World War II. Ascending the stairs to an empty attic, he is greeted by the comforting presence of Miep Gies and Mr. Kraler, dedicated office workers who had risked their lives to protect him and his family from the Nazis. As he embarks on a quest for his youngest daughter, Anne's diary, Miep promptly retrieves it, providing Otto with solace as he reads Anne's touching words penned three years earlier.
The scene shifts back to July 1942, where Anne begins documenting the oppressive restrictions imposed on Jews that force the Franks into hiding above a spice factory. In their concealed refuge are the Van Daans and their teenage son, Peter. Kugler, who works in the office below, along with Miep, his resourceful assistant, has orchestrated this clandestine haven, warning everyone that silence must be upheld during daylight hours while the workers are present. Kraler dutifully brings food and a box for Anne, gifted by Otto, containing her cherished photos of movie stars and a blank diary.
As the months fly by, Anne’s vibrant spirit shines through as she playfully teases Peter, whose only companion is his beloved cat, Mouschi. Otto takes on the role of teacher for Anne and her sister, Margot, while Mrs. Van Daan fondly reminisces about her youthful days and clings to the cherished fur coat gifted by her father. The tension of their confinement breeds disputes among the Van Daans, especially between Anne and her mother, Edith. One day, Kraler introduces a radio into the attic, granting the families a lifeline to the outside world. Soon after, he requests that they shelter another person: a Jewish dentist named Albert Dussell, who reveals the grim reality outside — friends vanishing, taken away to concentration camps.
A haunting moment occurs when Anne dreams of one of her friends in a concentration camp, waking up in terror. By October 1942, news of the Allied landing in Africa arrives, but the bombings of Amsterdam escalate. During Hanukkah, a sudden argument erupts when Van Daan insists on getting rid of Mouschi due to food shortages. Their quarrel is interrupted by a noise at the front door, sending the room into tense silence, only to break as Peter inadvertently tumbles over something while trying to catch Mouschi. The frightened intruder snatches a typewriter and escapes. A watchman, alerted by the commotion, summons two police officers who investigate the premises. Thankfully, Mouschi knocks a plate from the sink, leading them to believe the noise was merely caused by a cat, and they depart. Otto takes it upon himself to lift spirits by leading the group in a Hanukkah song of hope.
In January 1944, Anne captivates Peter’s attention as Miep brings a cake for everyone to share. Meanwhile, Van Daan requests Miep to sell Petronella's fur coat to purchase cigarettes. Kraler raises concerns regarding an employee’s odd behavior, hinting that their hiding place might be discovered. Dussell somberly notes that it is only a matter of time before they are caught. Anne expresses her frustrations towards the adults, blaming them for the war that has stripped away their dreams and ideals, leading her to flee the room, followed by Peter who comforts her. In a private moment, Anne shares her aspirations of becoming a writer while Peter laments his lack of ability to make a difference in the war.
Tensions flare when Van Daan attempts to swipe bread, only to be caught by Edith, who confronts him and demands he and his family leave the group. As conflicts over food erupt between Dussell and Mrs. Van Daan, news from the radio announces the Allied invasion of France, causing Mr. Van Daan to break down in shame. However, the good news reinvigorates hope among the group, prompting apologies for harsh words exchanged, while Anne dreams of returning to school by fall.
By July 1944, the invasion has stalled, and Kraler has been hospitalized due to ulcers. With the police having discovered the stolen typewriter, Anne begins to realize that her diary is her only means of preserving life beyond her death. As the Van Daans’ quarrels resume, Peter expresses his desperation and Anne reassures him of the goodness exhibited by those who have aided them. Their exchange is interrupted by the ominous sirens of an approaching police vehicle. Prepared for the worst, they share a passionate kiss amidst rising tension. As the German police brutally break down the door, Otto declares that they need no longer live in fear, but can embrace hope moving forward.
Returning to 1945, Otto recounts his harrowing journey back home after being liberated from Auschwitz to Miep and Kraler. The weight of grief settles in as he reveals the heartbreaking fates of Edith, Margot, the Van Daans, and Dussell, all lost to the horrors of the war. He holds onto a glimmer of hope that Anne may have survived, but he ultimately shares the devastating news of meeting a woman from Bergen-Belsen who confirms Anne's death. As he gazes at her diary, he reads aloud, >“In spite of everything, I still believe that people are really good at heart,” reflecting on Anne’s unwavering optimism amidst overwhelming despair.
