Honestly, at the beginning, I had the highest hopes of all three novels I read in this series, but in the end I lost to The Water Thief because the same plot twist was repeated several times in different versions. It's a cool story set in a confined location, which, surprisingly, conveys very well how scummy people become even more scummy under the influence of stress, the prospect of death and confined space (my respect). And although the main antagonists don't look so threatening at the beginning, the author does a great job with them and adds tension. Surprisingly, this plot section is divided into not two, but three branches, each separately for the Doctor, Amy and Rory. And Rory's adventures are the most interesting in the whole book.

Basically, a cool story that is weaker than The Water Thief, but stronger than Heart of Stone. I would call Rory's adventures and the way the author works with human characters its strength.