Doctor Who S9E3 - "Under The Lake" Recap

The year is 2119. In an underwater base, a military-industrial team find a vessel within a town that has long been submerged. They examine it and find mysterious symbols carved on the inside. One of the ship's engine actives and it ignites a fire. The group runs away but their commanding officer, Moran, is killed by a mysterious figure. They group turns around and sees Moran coming towards them in a ghost form along with the other apparition, who both proceed to attack the group.

Some time later, the Doctor and Clara arrive at the base, seemingly now abandoned. They eventually find the two ghostly apparitions seen before, who lead them to the ship. The Doctor and Clara go into the ship and find the same markings as before. The apparitions then chase after them with weapons and force the Doctor and Clara to retreat into a Faraday cage, where they meet the rest of the crew who have been hiding this whole time since the ghosts cannot get through those walls.

A deaf woman named Cass is now in charge of the crew, and she shares what happened before. The crew has no idea what caused any of this. The base shifts back into 'day mode,' during which they are free to leave the Faraday cage. For some unknown reason, the ghosts only appear and attack during the 'night mode.'

Thought initially skeptical of the idea of ghosts being real, he eventually warms to it and becomes excited. Later, the Doctor determines that the original ghost is an alien from Tivoli. The base switches to 'night mode' prematurely due to the ghosts taking over the base's functions and learning rapidly to maintain that control. The ghosts murder Pritchard, one of the crew members, and he turns to a ghost that attacks the group before another crew member is able to switch the base back to 'day mode.'

Cass wants her crew to abandon the base and calls a rescue sub before learning that one is already on the way. The ghosts had sent out a message in the hopes of getting more people they could convert into ghosts so the Doctor stops the sub from coming to the base, declaring it is under quarantine. The Doctor hatches a plan to trap the ghosts into the Faraday chamber, where Cass reads the ghosts' lips and determines they are repeating the same phrase over and over: "the dark, the sword, the forsaken, the temple."

The Doctor is able to decode the phrase as coordinates, and that the ghosts are transmitters sending signals to an unknown extraterrestrial destination. The signal is strengthened with each new ghost they create. The coordinates lead to a locked stasis pod hidden in a church inside the flooded town. The crew are able to retrieve it but can't get it open. The Doctor then realises that the symbols found earlier on the inside of the ship are the coordinates in written form. The writing also re-wires the synaptic connections in peoples' brains so that the ghosts are able to kill them and thus boost their signal.

The Doctor decides to travel back to when the ship first crashed in the town before it was flooded so that he may find out what is inside the pod as well as the meaning of the signal. The base begins to flood due to the ghosts tampering with the base's system and the group is forced to make their escape into the TARDIS. Unfortunately, the Doctor is separated from Clara and some of the crew members. He promises to save Clara, as well as Cass and Lunn, just as soon as he can figure out the message. The Doctor goes into the TARDIS with the crew members O'Donnell and Bennet. It's then that Clara, Cass, and Lunn spot a new ghost outside their window, that of the Doctor.

Doctor Who airs on Saturdays on BBC One.