The book begins with the ten Boom family celebrating the 100th anniversary of the family watch and watch repair business, now run by the family's elderly father, Casper. The business took up the ground floor of the family home (known as the Beje). Casper lived with his unmarried daughters Corrie (the narrator and a watchmaker herself) and Betsie, who took care of the house. It seemed as if everyone in the Dutch town of Haarlem had shown up to the party, including Corrie's sister Nollie, her brother, Willem, and her nephews Peter and Kik. Willem, a minister in the Dutch Reformed Church brought a Jewish man, who had just escaped from Germany, as a guest. The man's beard had been burned off by some thugs, a grim reminder of what was happening just to the east of the Netherlands.
In the next few chapters, Corrie talks about her childhood, her infirm but glad-hearted mother, and the three aunts who once lived in the Beje. She talks about the only man she ever loved, a young man named Karel, who ultimately married a woman from a rich family.
Eventually, both Nollie and Willem married. After the deaths of Corrie's mother and aunts, Corrie, Betsie, and their father settled down into a pleasant, domestic life. Then, in 1940, the Nazis invaded the Netherlands.
The family had strong morals based on Christian beliefs, and they felt obligated to help their Jewish friends in every way possible. The Beje soon became the center for a major anti-Nazi operation. Corrie, who had grown to think of herself as a middle-aged spinster, found herself involved in black market operations, using stolen ration cards, and eventually hiding Jews in her own home.
Corrie suffered a moral crisis over the lying, theft, forgery, and bribery that was necessary to keep the Jews her family was hiding alive. Moreover, it was unlikely that her family would get away with helping Jews for long, as they had nowhere to hide them. The Dutch underground arranged for a secret room to be built in the Beje, so the Jews would have a place to hide in the event of an inevitable raid.
It was a constant struggle for Corrie to keep the Jews safe; she sacrificed her own safety and part of her own personal room to give constant safety to the Jews. Rolf, a police officer friend, trained her to be able to think clearly anytime in case the Nazis invaded her home and started to question her.
When a man asked Corrie to help his wife, who had been arrested, Corrie agreed, but with misgivings. As it turned out, the man was a spy, and the watch shop was raided. The entire ten Boom family was arrested, along with the shop employees, though the Jews managed to hide themselves in the secret room.
Casper was well into his eighties by this time, and a Nazi official offered to let him go, provided he made no more trouble. Casper did not agree to this, and was shipped to prison. It was later learned he had died ten days later.
Meanwhile, Corrie was sent to Scheveningen, a Dutch prison which was used by the Nazis for political prisoners, nicknamed 'Oranjehotel'--a hotel for people loyal to the House of Orange. She later learned that her sister was being held in another cell, and that, aside from her father, all other family members and friends had been released. A coded letter from Nollie revealed that the hidden Jews were safe. While at Scheveningen, Corrie befriended a depressed Nazi officer, who arranged a brief meeting with her family, under the pretense of reading Casper's will. Corrie was horrified to see how ill Willem was, as he had contracted jaundice in prison. He would eventually die from his illness in 1946. Corrie also learned that her nephew, Kik, had been captured while working with the Dutch underground. He had been killed, though the family did not learn of this until 1953.
After four months at Scheveningen, Corrie and Betsie were transferred to Vught, a Dutch concentration camp for political prisoners. Corrie was assigned to a factory that made radios for aircraft. The work was not hard, and the prisoner-foreman, Mr. Moorman, was kind. Betsie, whose health was starting to fail, was sent to work sewing prison uniforms.
When a counter-offensive against the Nazis seemed imminent, the prisoners were shipped by train to Germany, where they were imprisoned at Ravensbrück, a notorious women's concentration camp. The conditions there were hellish; both Corrie and Betsie were forced to perform back-breaking manual labor. It was there that Betsie's health failed. Throughout the ordeal, Corrie was amazed at her sister's faith. In every camp, the sisters used a hidden Bible to teach their fellow prisoners about Jesus. In Ravensbrück, where there was only hatred and misery, Corrie found it hard to look to Heaven. Betsie, however, showed a universal love for everyone—not only for the prisoners, but also for the Nazis. Instead of feeling anger, she pitied the Germans, sorrowful that they were so blinded by hatred. She yearned to show them the love of Christ, but died before the war was over. Corrie was later released because of a clerical error, but she was forced to stay in a hospital barracks while recovering from edema. Corrie arrived back in the Netherlands by January 1945.