Doctor Who is always best when it does gothic horror, and that is something this Darksmith series has really focused upon, despite being intended for younger readers. Oddly, the main range of novels, intended for an older readership, has dallied very little with horror elements.
This is another very good read. As a novella rather than a novel, the plot isn't particularly convoluted, but the characters are well drawn and there are some effective set pieces. The plot is satisfying, with a gruesome and unpleasant villain and a steady escalation of menace, and it also advances the plot of the overall arc.
Not quite reaching the heights of the first two books in the series, but a very worthy read nonetheless.