Doc leaves Clara hanging in a haunted underwater research facility or military base or oil rig
The TARDIS is unhappy to have brought the 12th Doctor and Clara to an underwater research base in 2119 fully equipped with nuclear reactor, Star Trek references, quippy characters and a small but growing complement of ghosts bent on murdering anyone who enters the recovered alien spaceship in the loading bay.
There wasn’t always a lake where they are, however, and nearby is a submerged village slash military base slash underwater museum, its sole non-aquatic occupant a mystery that has lain entombed in a stasis pod since before the flood.
The spectral assassins only appear when the station goes into night-mode, and possibly but probably not to form a boyband, so the race is on to unravel this mystery and exorcise the base before digital dusk claims its next victim.
You asked for it, Michael. Here are the cards… ;-)