Okay, looking for the main plot of 'The Diary of a Young Girl' by Anne Frank? That's the one most people mean when they ask about a diary book. The core of it is the daily record of Anne Frank, a Jewish teenager, while she and her family hid from the Nazis in a secret annex in Amsterdam during World War II. It starts in 1942 when she's thirteen, and it covers over two years of confinement in a small, hidden set of rooms behind her father's office.
It's not just a historical document about hiding, though. The real plot is the internal, coming-of-age story happening under that immense pressure. She writes about her relationships with the other seven people in the annex—her often-strained connection with her mother, her love for her father, her budding romance with Peter van Daan, and the constant friction of living on top of each other. She details the boredom, the fear during air raids and burglaries, and the crushing anxiety of being discovered.
Simultaneously, the diary charts her fierce intellectual and emotional growth. She's painfully honest about her ambitions to become a writer, her thoughts on human nature, her faith, and her changing body. The 'plot' ends abruptly in August 1944 when the annex is raided and the occupants are arrested. The final, haunting note isn't written by Anne but by a postscript stating her eventual death in the Bergen-Belsen concentration camp. The power comes from knowing the ending she never got to write herself.