'Doctor Who' recap: Treebeard's Christmas Vacation
The Doctor and Cyril's sister Lily go looking for him, and then Madge goes looking for them. While the Doctor and Lily encounter the tree people, Madge meets some folks from the military industrial complex of that planet and learns that these trees are about to be converted into a fuel source. This involves melting them with acid rain, of which the trees are aware and eager to escape. This is why they've lured Cyril to them, but then they realize that Cyril is too "weak" to carry their "life force" off the planet. Much the Doctor's chagrin, they also determine that he's too weak. Lily, they decide, is strong, but too young.
Cue Madge's entrance, as she somehow manages to drive a giant robot and find her offspring. Madge is just the vehicle -- or "mother ship" as the Doctor puts it -- that the trees need. She carries them off to the time vortex and then manages to get everyone else back to Earth under the Doctor's guidance. He tells her to wish super-duper hard for home, but she inadvertently brings up an image of her husband about to crash to his fiery death. Her children realize she's been keeping a secret from them, but lo and behold, she's also somehow managed to guide her husband's plane safely home, as well. Everybody lives! Madge realizes the Doctor is the spaceman she helped years earlier. With Madge's encouragement, the Doctor decides to pop in on Rory and Amy for a Christmas visit. There are hugs and happy tears and a full weecap to come.