Jerry L. Walls 
Purgatory [PDF ebook] 
The Logic of Total Transformation

In Catholic theology, purgatory has been understood as applying to persons who are already in a state of grace or salvation. In popular thought, however, it is sometimes understood as a "second chance" for the unconverted. In this book, a follow-up to his earlier Heaven: The Logic of Eternal Joy and Hell: The Logic of Eternal Damnation, Walls completes his examination of the Christian theology of the afterlife with a inclusive and multi-denominational analysis of the doctrine of purgatory.