Defenses of what? I need a specific topic.
I could refer you to defenses of icons, of veneration of the God-bearer, of the word “God-bearer” as her title, of episcopal governance, of Orthodox ecclesiology, of the doctrine of the Trinity, of the homoousion, etc., but I don’t know what you want.
Typically, short introductions are going to be from one confessional perspective (Orthodox, Catholic, Lutheran, Calvinist, Fundamentalist, etc.) or another. Again, please be more specific.
It’s a big question, and to ask it as you have is a bit like saying, “Can someone please give me a recommendation of an introductory book on knowledge?”