Sophies World by Jostein Gaarder
Read this book several years ago and I loved it! Below is amazon.coms synopsis of the plot.
Wanting to understand the most fundamental questions of the universe isn't the province of ivory-tower intellectuals alone, as this book's enormous popularity has demonstrated. A young girl, Sophie, becomes embroiled in a discussion of philosophy with a faceless correspondent. At the same time, she must unravel a mystery involving another young girl, Hilde, by using everything she's learning. The truth is far more complicated than she could ever have imagined.
betweenworlds
Everything secret degenerates, even the administration of justice; nothing is safe that does not show how it can bear discussion and publicity. Lord Acton 1834-1902