Tonight's episode "Flatline" begins with a man disappearing from his home after announcing "They are everywhere." Later, the Doctor tries to get Clara home after another adventure, except they end up in Bristol, quite a ways from where she lives. More confusingly, the Tardis has shrunk and they have to squeeze through the doors to get out. The Doctor sends Clara away while he searches for the cause of this strange malady. She goes for a walk and encounters a graffiti artist doing community service named Rigsy. In a funny scene, she takes up the mantle of the Doctor and pokes fun at her traveling companion. Rigsy then comments on a number of people who have gone missing. Also painted on the wall are a bunch of people with their backs to them.
Clara returns to the Tardis and finds it's shrunk down down to about the size of a soda can. She thinks it's funny, but the Doctor--who's now trapped inside--isn't so amused. He reveals that something is leeching external dimensions, and its coming from the northwest. Clara puts the Tardis in her purse and meets up with Rigsy, and the two of them investigate a flat where one of the people disappeared. It's a locked room mystery, and they set about solving it. Soon Rigsy decides to return to his community service, but the Doctor finds him useful, so he has Clara show him the Tardis to get him to stick around. Suddenly, the Doctor announces that an unknown force is sucking the Tardis' energy.
Afterwards, Clara and Rigsy head to the site of another disappearance where they meet MI5 agent Forrest. The agent goes into another room, but a writhing something sucks her into the floor. Clara and Rigsy rush in to assist, but they're too late; Forrest's nervous system has been scaled down and flattened along the wall. The Doctor realizes they're dealing with two-dimensional life forms who are dissecting humans to understand three-dimensional organisms. The 2D entities move in to attack them, but they get on a chair suspended from the ceiling to avoid getting caught. Danny calls and asks if everything's all right. Clara lies to him and says yes, and they escape through the window.
They return to Rigsy's community service detail, only to find the people painted on the walls coming alive. The Doctor declares these are the missing people, and the 2D beings are wearing them like camoflage. The group escapes into a warehouse with the invaders in pursuit. The Doctor wants to try communicating with them because they may not realize they're doing humans harm with their experiments. Using the sonic screwdriver, they rig the building's PA system to transmit a message. The 2D beings respond using numbers, which the community service detail realizes are the numbers on their jackets. Are the invaders listing their past and future victims?
After another attack, one of the men bites it, and the group escapes into a tunnel system. However, they find all doors have been turned to 2D. The Doctor, still stuck in the Tardis, comes up with a device he calls a Toodis which can restore a door handle to 3D. They move deeper into the tunnels, but a giant hand reaches out and grabs another of the workers, revealing they're evolving into 3D. The group makes a run for it, but Clara gets bumped and drops the tiny Tardis into a hole, where it lands on subway tracks...and there's a train coming. There isn't enough power left in the Tardis to defend against this, and the Doctor seems doomed. But taking advice from Clara, he sticks his hand out and maneuvers the Tardis out of the way like Thing from the Addams Family. The Tardis then goes into siege mode, essentially turning it into an impregnable cube. Unfortunately, life support is failing, and it desperately needs a recharge.
No longer able to communicate with the Doctor, Clara has to find a way out of this on her own. So she has Rigsy draw a picture of a 2D door and places it along a wall in the tunnel, and she puts the Tardis behind that wall. The 2D beings poor energy into the faux door trying to get through it, unknowingly powering up the Tardis behind it. Now re-energized, the Tardis goes back to full size, and the Doctor comes out and condemns the 2D beings which he has dubbed Boneless. They knew exactly what they were doing, making them monsters. And if they insist on being monsters, then the Doctor must become "the man who stops the monsters." He banishes the Boneless back to their own dimension and then gets the workers back to the surface. Afterwards, Clara tells him to admit she made a pretty good Doctor. He admits she was a fine Doctor, but says goodness had nothing to do with it. She keeps lying to people throughout this episode, and he doesn't seem to approve.
Finally, Missy appears and has taken a keen interest in Clara. What's going on here? We'll just have to wait to find out.
I found this week's episode to be very imaginative. The 2D beings idea, while not wholly original, was executed very well. And the Doctor's subtle commentary on his own nature speaks to the quality writing this shown continues to display.