BY Peter Kreeft
This is one of the best introductions to philosophy on the Internet. The audio version is for sale on audible and amazon. You can download the zipped version of the book from Audible with this link. The notes are very similar to the actual audio, but it is so good to just listen to Kreeft himself explain it and it is so well put together.
This is the best introduction to the Philosophy of St. Thomas Aquinas. There are summaries for each chapter that are stepping stones into the Summa Theologica itself. The Summa Theologica is Aquinas' greatest work. It is a complete synthesis of Catholic Theology, philosophically based.This book's summary has chapters. Normally these will match the chapters of the book:
Peter Kreeft. The Philosophy of Thomas Aquinas, Boston:The Modern Scholar, 2009