This is the fourth and final instalment of the Timewyrm cycle and sort of brings the entire series full circle. The Timewyrm begins the cycle as a cybernetic organism who calls herself Ishtar, and finishes the cycle as a baby who is given the name Ishtar. It appears that the Doctor (and the authors, because all of these books are written by different authors) have created what appears to be a time loop, and the Timewyrm simply exists is a cyclical entity going from Timewyrm to Ishtar and back again. The whole concept, when you put your mind to it, really does your head in.
There is not really much more that I can say about this book. The Doctor and Ace arrive in a village, but it turns out that the village is on the moon, and when they step outside they die and go to hell, though it is not hell but some alternate dimension (hold it, isn't that what Hell actually is? An alternate dimension). In the church there is some disembodied voice called Saul who has inhabited the region long before the church began, but I do not believe that it is the Timewyrm (though I believed that it was when I first read the book). It turns out that the Timewyrm is actually a childhood bully of Ace's.
The books do get better from this one, though this story arc was not all that bad. This book appears to be the first to really push the boundaries of the new style that Doctor Who had taken. We must remember that during the days of the old series there were no extra novels but rather novelisations of the actual TV shows. Though a few novels were written regarding shows that were either not made, or incomplete (and when Tom Baker retired, he retired for good), they were generally novelisations. I know that the Star Wars and Star Trek franchise do release a number of novels (I assume one per month, but I will check that up later, and I cannot, for the life of me, remember which ones that I have read. That is okay because I would rather not embarrass myself any further by actually admitting that I read a Star Trek novel).