As the title says, this is a book about the "Music" of Pythagoras; and is concerned with the biographical, musical, and philosophical aspects of the Pythagoreans. If one is looking for a more mathematical treatment, see Maor's "The Pythagorean Theorem." A few of the chapter subtitles reveal the tone of the book, "At the hinge of legend and history," "All things known have number," "Plato's Search for Pythagoras," "Wherein Nature shows herself most excellent and complete," "'While the morning stars sang together': Johannes Kepler," and "The Labyrinths of Simplicity."
The reading was a little slow going midway, addressing the weight of previous scholarship. One senses an extra effort to be fair-minded, but the upside result of this deliberation was a more intense focus on what is essential and relevant about Pythagoras and the Pythagoreans today. This carries us far beyond the "series of facts" mentioned by the editorial review from Publishers Weekly. The last few chapters are the best, written with wit and insight. Pythagoras appears through the contrasting viewpoints, questions, and speculations by musician and author Kitty Ferguson. Arthur Koestler sums it up with a quote about the Pythagorean vision, "Cosmic wonder and aesthetic delight no longer live apart from the exercise of reason."
Some mathematicians tend to write dismissive works such as Bell's "The Magic of Numbers" or Dudley's "Numerology: Or, What Pythagoras Wrought." And some philosophers tend to be overly critical, e.g. Bertrand Russell. It is among musicians where you generally find the true spirit of Pythagoras, and the in-depth research of the code mentioned in the subtitle.
From the excellent references in Guthrie's "The Pythagorean Sourcebook and Library" and Godwin's "The Harmony of the Spheres: A Sourcebook of the Pythagorean Tradition in Music" one can find the work of Thimus, Kayser, Haase, and other musicians. Many scientists from Newton to Einstein have also embraced much of the Pythagorean legacy of an order and harmony in the foundational nature of the universe. The deeper mathematical code is perhaps too esoteric for general readership, see Bamford's "Homage to Pythagoras"; and from musicians Ernest McClain and William B. Conner, deeper explorations. And authors who go even further, Manly P. Hall and Franklin Merrell-Wolff.