Some blanch at the idea of mixing the universes of Doctor Who and H.P. Lovecraft. What few realize is that the two mythos are already intertwined, with The Great Intelligence (the primary villain of the second half of Series Seven) having originally been given the name Yog-Sothoth back in The Second Doctor era. Indeed, the episode The Web of Fear mentioned The Great Old Ones by name!
A lesser writer might have limited themselves to the gimmick of The Doctor getting his hands on a copy of a forbidden book but Michael Scott does far more to take this story beyond its novel concept. The characters of The Second Doctor and Jamie are perfectly captured. And Scott's prose perfectly emulates the weird horror of the Lovecraftian setting.
If you're a fan of Lovecraft who isn't familiar with Doctor Who, this story is a wonderful introduction. If you're a fan of Doctor Who in general and The Second Doctor in particular, it is a must read.