The Doctor and Clara return this week on "Journey to the Centre of the TARDIS."
The episode opens with the Doctor teaching Clara how to operate the TARDIS, and disables the shields in order to turn on "basic mode." This is some unfortunate timing, as just then, the TARDIS is caught in the magnetic tractor beam of a salvage ship. Clara then spots a weird egg shaped object rolling about, but burns her hand when she goes to grab it. Before we can find out what it is, the ship takes a hit and the two are knocked unconscious.
The Doctor wakes up on the salvage ship, and meets the crew: Gregor Van Baalen, his brother Bram, and an android named Tricky. convinces the crew to help him rescue Clara by saying it would allow them to salvage the rest of it. Once on board the TARDIS again, the Doctor pulls a fast one by removing the doors and starting a self-destruct timer. With the clock ticking, the group ventures into the ship in search of Clara.
Gregor tries to figure out how much the ship is worth, but the Doctor warns him that removing pieces of it will make the TARDIS quite angry. This is succinctly demonstrated when the TARDIS traps them in an infinite loop of corridors when they remove part of the architectural reconfiguration system. Despite the obvious warning, Gregor tells his brother to break down the console. As Bram gets to work, he's killed by a mysterious skeletal creature.
We then get a chance to see what Clara is up to, as she awakens in a TARDIS corridor, and unsuccessfully tries to navigate about. As she gets more and more lost, that mysterious monster from before gives chase, forcing Clara to take shelter in various rooms, including the TARDIS library. She notices that the burn she suffered earlier is seemingly turning into letters of some sort. As she continues to wander the TARDIS, she ends up in the console room, where another monster waits.
The Doctor and the salvage crew reach the console room and save Clara, before it's revealed that the engines have become unstable due to a time leak, and they will need to get to it in time before it explodes. Unfortunately, the monsters have them cornered. It's then the Doctor realizes that the creatures are actually them, from a far distant future where they've become trapped by the time leak. Gregor and Tricky are touched by their future versions and turned into one themselves, forcing Clara and the Doctor to continue on their own.
They reach the engine room, and find it has already exploded, but that the TARDIS has placed the room in a time stasis. The duo then see that the burn on Clara's hand is a message from the TARDIS itself, telling them to find the "big friendly button." The Doctor realizes this is the egg device from before, and takes it through a rift in time back to before all of this. He warns his past self, who presses the "big friendly button" on the device, resetting time to before the episode started.
The salvage ship carries on, not noticing the TARDIS (although it seems the characters have changed for the better), and the Doctor and Clara recoup, ready for their next adventure.
They'll return in "The Crimson Horror" on May 4, and will be the 100th broadcast episode since the series was relaunched.