The episode opens with a scan across thee top of a large underwater base station. Inside, there are several crew members discussing the discovery of a futuristic looking jet they have brought on board. Inside, there are four words marked on the wall in a foreign language. The words seem to imprint onto the eye when looked at, hinting that they are going to mean something later in the episode. After the appearance of a ghost like creature, the crew run down claustrophobic long corridors, only to be confronted by their fellow crew member who is now himself, ghost like.
The TARDIS brings the Doctor and Clara to the ship, and the Doctor does eventually admit that these creatures are, in fact, ghosts. But have we seen this story before? Cold War was similar in may ways, with the cliche crew who aren't getting along and no where to run, however this episode does stand alone with its own quirkiness. Crew member, O'Donnell is huge fan of the Doctor which offers a satirical side to the episode. In a mix of the Doctor trying to sign to a deaf crew member and Clara's reminder to the Doctor to use his cue cards in a time he needs to offer comfort, this dark episode remains lighthearted.
The crew members begin to be killed off one by one, all turning into the ghost figures and all muttering four words silently. The smartest person on board seems to be the deaf crew captain who decides it's time to return to land, except the ghosts have already sent for a rescue crew, proving that they need more bodies.
The four muttered words turn out to be coordinates to a church and also the markings on the inside of the salvaged ship. The church is now underwater so of course, the Doctor will need to travel to it in the past ... But that's next episode. Ending on a cliffhanger again - which I won't spoil because it's too good - I'm forced to question: Why have we already had two 2-part episodes? Is the script pile running so thin?
All in all, the episode offers the typical creepiness of the Doctor in a confined space within a recycled story. The only difference: The Doctor has admitted to ghosts being real. But why?