The Frank family goes into hiding in the Secret Annex behind Otto Frank's business at Prinsengracht 263 in Amsterdam. They are initially extremely cautious and fearful of being discovered.

The van Pels (van Daan) family, consisting of Hermann, Auguste, and their son Peter, joins the Franks in the Secret Annex. This increases the challenges of living in such a confined space.

Daily life in the Annex is characterized by strict rules, limited resources, and constant fear of discovery. The inhabitants must remain quiet during the day to avoid being heard by workers in the warehouse below. They spend their time reading, studying, and trying to maintain a semblance of normalcy. Tensions often arise due to the confined space and differing personalities.

Fritz Pfeffer, a dentist and friend of the Franks, joins the inhabitants of the Secret Annex. He shares a room with Anne, leading to further friction and difficulties.

Otto Frank's trusted employees, including Miep Gies, Johannes Kleiman, Victor Kugler, and Bep Voskuijl, risk their lives to provide the inhabitants of the Secret Annex with food, supplies, and news from the outside world. Their courage and dedication are crucial to the survival of the hidden families.

Despite the difficult circumstances, Anne experiences significant personal growth during her time in hiding. She matures from a young girl into a thoughtful and introspective teenager. Her diary reflects her evolving views on life, love, and the world around her.

The inhabitants of the Secret Annex live with constant fear and uncertainty. They rely on news broadcasts and the accounts of their helpers to stay informed about the war. Rumors of arrests and deportations add to their anxiety and despair.

The Secret Annex is raided by the Gestapo. The eight inhabitants are arrested and taken to Westerbork transit camp, ending their time in hiding.