Tonight's episode "In the Forest of the Night" begins with the Tardis landing in the middle of a forest. A little girl named Maebh approaches and asks the Doctor for help. She explains she was with Danny Pink, but someone told her to come here. Confused and a little irritated, the Doctor takes her into the Tardis, where she seems unimpressed at its dimensions. He complains he can't get to the center of London, but Maebh tells him they are in the center of London (Trafalgar Square, to be exact). But how can this be? It's a forest, not London.
Meanwhile, Clara, Danny and their students are leaving from a sleepover at the London Zoological Museum. They step outside and find the entire city overtaken by a forest that grew overnight. Turns out, it's not just London; it's the entire world. Clara calls the Doctor to tell him, but he already knows. He tells her he has Maebh, but when Danny asks, Clara lies to him about who she was talking with.
The group heads to the Tardis and seeks shelter inside. The Doctor doesn't appreciate all the kids poking around, but forgets about that when Maebh once again goes missing. Clara explains the girl's sister also went missing, causing Maebh to become borderline autistic and hear voices. Seeing a clue there, the Doctor decides Maebh holds the key to solving this mystery. He soon finds her homework, on which she has predicted a coming solar flare. How did she know about it?
The Doctor and Clara go outside to search for her, and they run into men in hazmat suits who are attempting to burn down the trees. However, the trees turn out to be fireproof. The two continue on, but are soon chased by wolves that have escaped from the London Zoo. They eventually run into Maebh, but things get much worse when a tiger shows up. Fortunately, Danny arrives and scares it off with a flashlight.
Maebh reveals she is the one who summoned the trees. Thoughts just come to her, she says, and she thought it would be nice to have a forest. Suddenly, an imposing voice begins speaking through her. Calling itself the Here, it says it has been on Earth long before everyone else, and it will be on Earth long after everyone else has died. Furthermore, it says the sun has called it. The Doctor declares that because of the impending solar flare, the planet is doomed. Clara suggests he use the Tardis to save the children. But it's just a trick to get him to save himself.
The Doctor takes off, leaving everyone to their fate. Upon further examination of the situation, though, he has an epiphany, and quickly returns. He tells everyone the trees are actually a defense mechanism meant to save the world. Sure enough, the massive supply of oxygen they've built up protects Earth from the solar flare, and the trees disappear. Watching this unfold is Missy, who seems impressed.
Everyone rejoices at their salvation. The Doctor reveals this has happened numerous times throughout human history. Mankind remembers the fear (which is why we're afraid of the forest), but not the cause. Finally, Danny tells Clara to stop lying to him about her adventures with the Doctor.
Oh, and Maebh's sister comes back.
Tonight's episode, like most of the ones this season, was solid. I thought the sudden forestation of the planet was an original storyline, and Peter Capaldi continues to impress with his gruff, snarky interpretation of the Doctor. Also, I like how Clara is an imperfect character; she continually lies to her friends, and it keeps getting her in trouble. I sense they're building up to something with her, and I look forward to finding out what.
Next week is the first of the two-part finale.