The Rest of the Bible is about what Protestants usually refer to as the "Apocrypha." (In the Roman Catholic Church, these books are known as the Deuterocanonicals, which name was given to them after the Counter-Reformation Council of Trent and in an effort to acknowledge Protestant objections. Prior to that, the books were simply part of the Old Testament.) Author Theron Mathis (great name!) takes the reader through these books, summarizing each and then explaining its context for the Church fathers and why these books are part of the Orthodox Scriptures. I also learned that St Athanasius referred to these books as "Anagignoskomena," or the "Readables." I like that.
All in all, this is a fairly brief, as well as very interesting, read. I grew up believing these books had been "added" along the way, so I honestly have never cracked them open, even in my Orthodox Bible. (It turns out that they weren't added, but instead removed. More specifically, the current Protestant Old Testament reflects the grouping of the 10th-century Hebrew Masoretic Text instead of the earlier Greek Septuagint.) Reading The Rest of the Bible gave me a frame of reference for reading them and helped me to understand why they are considered an important part of the Old Testament Scriptures.
Again, the book is written by an Orthodox Christian, but he is obviously reaching out to those who are unfamiliar with the books (and without any obvious desire to proselytize), so I'd recommend The Rest of the Bible for anyone who is interested in finding out a little more about the books that, for many, got left behind.
A quick listing of the books that Mathis discusses:
The Prayer of Manasseh
Esther (parts of it are not included in the Protestant canon)
1, 2, and 3 Maccabbees
The Wisdom of Solomon
The Wisdom of Sirach
The Epistle of Jeremiah
Daniel (added parts: Susanna, Songs of the Three Holy Children, Bel and the Dragon)