This old yet revised work (3rd ed.)offers an excellent introduction to the writings of a reliable non-determinist. You will enjoy reading this book, and although newer volumes call on an even greater range of supporting material, his bibliography is excellent and arguments strong.
This book primarily engages with the Calvinist/ Arminian debate and argues both sides effectively, but because of the Biblical evidence leans towards non-determinism.
I have yet to read anything by Marshall that has disappointed me.