Bill decides to move in with some of her friends into a new house-after a few false starts, they eventually get a low cost mansion-provided they stay out of the tower.
The Doctor wants to help Bill move her stuff in, but the Doctor notices something ‘off’ about the house-and then one of the tenants vanishes when playing music, and there’s a strange knocking noise. Nevertheless, Bill and co. assume it’s nothing. But then more people start vanishing-turns out they’re being consumed by tiny alien bug monsters called the “Dryads”
The Dryads-who are activated by sound, such as the Landlord’s tuning fork, feed on the building’s tenants to sustain the inhabitant of the tower, Eliza, who is actually become a wood creature. The Landlord’s memory is a bit off, and he initially thinks Eliza is his daughter, but she is in fact, his formerly terminally ill mother, who was ‘saved’ by the alien bugs
Although ‘healed’ from her illness, her body has become mostly wood and she has to stay in the house. However, she’s tired of staying in the house and costing people’s lives, so she embraces her son and they are both consumed by the bugs, restoring Bill’s friends (although not the earlier inhabitants) and destroying the mansion.
Meanwhile, the Doctor continues to keep his vigil on the vault-and we learn that the inhabitant-who plays piano-finds the story-especially about people being consumed-very exciting. Gee, I wonder who it could be?
The Doctor-bored on being stuck on Earth guarding the vault-decides to head out to space despite the objections of Nardole. They land on a mining station where oxygen is precious-worth money even-and due to an apparent malfunction-but actually programming from the company-the spacesuits (Called “Smartsuits” kill their wearers, and work to do the same to others-effectively making them a sort of zombie. The only survivors are wearing suits that are somewhat damaged.
The Doctor and the survivors try to figure out a way to save themselves, but during an attempt to escape, Martha’s suit malfunctions, and she is exposed for several seconds to the vacuum of space.
The Doctor saves her by giving her his helmet, but unfortunately as a result is partially hurt by the vacuum himself-leaving him blind.
The suit also seems to kill Bill as well, but the Doctor wires the computer to self-destruct the station, but at the last minute is able to reason with the smartsuits that their deaths and the destruction of the station would be expensive for the company controlling them, so he’s able to save them (and give the crew some needed oxygen). The TARDIS is eventually recovered, as are (apparently) the Doctor’s eyes-and the crew is dropped back at corporate HQ, for a chat with their ruthless employers.
Back on Earth, Nardole scolds the Doctor for nearly getting them all killed this time-and leaving the vault unguarded, which could have grave consequences if the inhabitant escapes. Nardole asks him to look at him, but the Doctor can’t. Although his pigment has been restored….he’s still blind!