Ian alerted me to this novelisation (published in 1986, of a 1968 story) as being possibly one of the better ones of the later Target run, and I got it off eBay pretty easily. I admit I (and even more so my wife) had found the original story a bit lacking; since then, however, I've seen the few surviving clips on the "Lost In Time" DVD and it really does look much better than it sounded. Also, in the context of a Doctor Who which was moving more to contemporary England as a setting, it makes more sense; it is a successful (and maybe in some ways better) prototype for some of the Pertwee stories. (Drilling-awakes-ancient-enemy of course goes back to Lovecraft and before, but reappears in Who in Inferno and The Power of Kroll at least.)
Anyway, the book is OK, and as you can see has prompted me to re-evaluate the original story, but it is not a great work of literature. As with too many of the Target novelisations, it is mostly narrated as if the author were simply writing down what is visible on the TV screen, and Pemberton's occasional excursions into tight third are actually jarring and often unsuccessful. The Doctor and companions get apparently killed so often that it loses dramatic impact (and this occasionally calls forth thunderously bad prose, citing for instance pp 129-130). On the other hand, the book does make more sense than the original story and fills in some of the plot gaps and backgrounds to the characters, and Victoria's decision to depart is decently foreshadowed. And the monster, as so often, is more convincing on the printed page. So I don't regret buying it.