Cyril makes his way into the dome portion of the lighthouse. The door closes behind him. Beyond there is a throne. A tree woman stands over it, a wooden grown atop her head and a thin gold circlet in her hands. Lily and the Doctor race into the lighthouse and find Treebeard. The Doctor sees the tracks and surmises this was what Cyril was following. The Doctor gets all flustered the way he does when he sees clever things, because the entire building is made of trees that have grown together just so. He also surmises that the whole thing with its very tempting doors is a "people trap," but why would a forest need people? Maybe to hear when a tree falls.
Back at the robot thing, Madge's sobbing has affected the workers. After some comedic arguing, they decide to lay down their weapons and make their introductions. They're from Androzani Major in the year 5345. Madge introduces them to the gun she's been hiding in her coat. "Crying's ever so useful, isn't it?" she asks with a sly smile.
The Doctor isn't having much luck getting to Cyril because he can't sonic his way past the wooden door. Lily points to a window and to the trees beyond as thousands of lights rise up out of their branches. The Doctor calls it "pure life force." Lily is so awed that she cries a bit. "Crying when your happy," the Doctor says, "good for you." He gives her shoulders a squeeze. "That's so human!" Inside the dome, the tree lady places the circlet on Cyril's head. Treebeard gets up creakily from his throne and clomps his way upstairs.
Madge has gotten the woman worker to tie up her coworkers in the cockpit of the robot thing. Madge recognizes it as a cockpit because, as she says, her husband was a pilot. I can't see much similarity between a 1941 airplane and anything from 5345, but whatever. The woman then goes to the computer to scan for Madge's children. The others tell her that the forest is about to be "harvested," because Androzani trees are the greatest fuel source ever. "The entire area is being melted down for battery fluid." This will be done by the acid rain that's due to fall in five minutes.
The Doctor and Lily get into the dome and find Cyril unconscious. Through a window, they see the life force leaving the trees and heading for the dome. Cyril rouses and speaks for the wooden king and queen. "They're scared. Can't you hear them? The trees are screaming."