Vallée's The Shaping of Christianity, The History and Literature of Its Formative Centuries (100-800) is a brief introduction covering the period after the time of The Twelve and before the Mideaval period. While I could pick a few nits (which I won't here), it is hard to imagine how a book of its size could be better for its intended purpose than the present work.
The text reads easily and whilst there is some jargon and reference to various historical events Vallée provides a glossary, timelines and footnotes. Each chapter begins with some introductory text and concludes with a list of readings. The final chapter, "Conclusion", wraps up the text. There are several Appendixes for those wishing to see what is available to pursue further studies.
The book receives my strongest recommendation to those who aren't specialists who would like a historical sense of the development of various flavors of Christianity. Indeed, it has been my observation that among various Christian traditions these days claiming to be of a Bible-believing bent there is almost total ignorance of the subject matter this book covers. To these folk I urgently recommend this book so you can get a sense that the beliefs you feel are so obvious from the Bible don't just jump off pages of the Bible like you may think, but rather have some history behind them.