Instead of returning Amy and Rory to Leadworth for Christmas as he had promised, the Doctor accidentally lands the TARDIS on an Earth-like planet during winter.

A young woman named Bel Flurrish believes they are connected to her missing sister Vesta, who disappeared the previous night.

Amy is separated and then attacked by rat-like creatures; the Doctor uses a high-pitched sound from his screwdriver to render them unconscious and explains they are genetically engineered rats made by the Morphans' terraforming system and are responsible for the dead livestock.

Exploring the terraforming plant, the Doctor finds a device which is able to transport holograms of them to the assembly hall when Rory, Vesta, and the other Morphans are.

Before returning to the TARDIS to take Amy and Rory home for Christmas, he informs the Morphans that he reset the Guide to make it more user-friendly, and they will have the option to choose when they let their ancestors out, if at all.

[1][2] Will Salmon of SFX gave the book four out of five stars, labelling it as "tells a spooky monster story that’s big on atmosphere, if lacking in originality".

[3] Den of Geek's Mark Harrison gave it three out of five stars, questioning whether the extra page length was necessary for the story, though he thought it was "very well-written".

He praised Abnett's description of the Ice Warriors, but he thought it "unfortunate...that the story itself runs out of steam after a few early encounters with the green giants".