Music is one of the oldest art forms, and yet due to its intrinsically ephemeral nature we are unable to reconstruct almost anything from the earliest music. Only after the musical notation has been devised (some time in the early second millennium AD) can we begin to understand what musical performances were like. Nonetheless, for the longest time musical notation was used primarily as a musical guide, and not as a definitive representation for any given musical piece. Even in the recent centuries, when the notation became increasingly sophisticated and detailed, we are still largely left in the dark about how exactly any given piece of music was originally performed. All these systemic difficulties stand as an obstacle to our fuller understanding of the early music.
This very short introduction does a very thorough job of introducing the reader to the early music. It is aimed at the interested non-specialist, but it still adheres to the rigorous academic methodologies when approaching its subject. The book is tremendously informative and comprehensive, as much as such small format will allow. However, due to its subject matter and the relative obscurity of many of its concepts and themes, it is not the most readable of introductions. If you are a music nerd or intrinsically enjoy all aspects of musical history and theory, then you'll certainly enjoy this book. If you are a general reader on the other hand this book might be a slow read. It is still a pretty good book, as long as you understand exactly what it aims to do.