Parts: 1 (45-minute)
Writers: Frank Cottrell-Boyce
Airdate: 25 October 2014
Production Code: n/a

Doctor: twelfth
Companions: Clara

Story: After a successful overnight trip to the London Zoological Museum, chaperoning a group of Year 8 Coal Hill students, Clara and Danny round up the children to take them home... but their plan suffers a massive setback when they walk out of the museum to discover that a gigantic forest has grown up in central London overnight.

The Doctor, in London for reasons of his own, has also discovered the forest's existence. Not only does it cover London, it blankets the entire world. With the inconvenient trees bringing civilization grinding to a halt, the Doctor and the Coal Hill group must uncover the truth about the mysterious forest's sudden appearance.