It's interesting to see McCormack try out a concept she will later nail in Caged (with the 15th Doctor). It's clear that she likes to think up a good alien species with a unique world and outlook. But it just works so much better in her later book. Contrasting the two demonstrates why.

In Caged, just as in Molten Heart, we start with the main character. In both cases, an adventurous young girl somewhat at odds with her small community by dint of her adventurousness. But in Molten Heart, we stay with this character for just one short prologue chapter before the Fam arrives. In Caged, it's a good chunk of the book. We get a real feel for our heroine. We are rooting for her and care about her before the Doctor and their companion(s) arrive. There is no such feeling in Molten Heart.

The emotional beats hit harder in Caged. It gives us the confusion of an alien abduction and the doubts of the abductor and we feel both. Molten Heart gives us only what we can see coming a mile away.

This makes Molten Heart fascinating, because in it we can see the rough draft of some ideas that are better realized in McCormack's later, excellent book. I'm an Una stan and it's cool to see her improve from this book, which I didn't care for, to the other book, which is among my top DW novels.

Separately, this book once again underlines a problem with the Fam. The TARDIS has too many people and they never get interesting development. This book should have sidelined two — and I mean really sidelined; have them left at home on the TARDIS playing a game that we cut back to for ten pages total — and focus on just 13 and Ryan or just 13 and Yaz. I would love a larger TARDIS team that played with this and if it won't happen in the show, maybe it ought to happen in these spinoff novels.

I really dug this adventure (pun intended) the first half of this adventure. I feel like the relationships and dynamics between the TARDIS team are the strongest I’ve ever seen them, and honestly exactly what I want from a 13th Doctor novel. On the other hand, once we get into the classic who style cave runaround for the majority of the novel, I definitely checked out emotionally. Cool book, but I lost interest about halfway through and I never got it back.