[[quoteright:350:http://static.tvtropes.org/pmwiki/pub/images/lighthouse_7571.jpg]]
->''[[ExpospeakGag The localised condition of planetary atmospheric condensation caused a malfunction in the visual orientation circuits. Or to put it another way, we got lost in the fog.]]''
-->-- '''The Doctor'''

Season fifteen kicks off where season fourteen finished: GothicHorror. The TARDIS materialises in a lighthouse on an isolated piece of shoreline just after a mysterious light has been seen falling from the sky. One of the lighthouse-keepers is found electrocuted. The Doctor and Leela (who throws on a nice warm sweater) investigate.

Soon, a sudden fog bank descends, causing a ship to founder on the rocks. The posh survivors straggle ashore but they soon find that they're locked in the lighthouse with a Rutan -- a jelly-like alien '''''[-[[http://www.youtube.com/watch?v=tWdgAMYjYSs SSKK!]]-]'''''

'''''[-[[MaxHeadroom That does it! He's a frigging nerd! Heeheehee!]]-]'''''

'''''[-[[http://en.wikipedia.org/wiki/Max_Headroom_broadcast_signal_intrusion SSKK!]]-]''''' that can take other forms and has been masquerading as lighthouse-keeper Reuben.
The Rutans are described by the Doctor as being the ancient and implacable enemies of the Sontarans, who have appeared multiple times in the show's history (though this is the only appearance so far of the Rutans). Everyone who's not on team TARDIS dies. The Doctor kills the Rutan warrior with a makeshift explosive, and then uses a diamond that one of the survivors had been carrying to focus the lighthouse's light into a laser beam to destroy the incoming Rutan mothership. Despite the Doctor's warning, Leela looks at the explosion and gets blinded. She promptly tells the Doctor to kill her, because she's a liability, but he explains that the blindless is temporary -- although it did change her eye color permanently, from brown to blue.

!!Tropes

* ActionGirl: Leela has already shown herself to be one, but she's particularly BadAss in this episode, slapping a character who goes into hysterics and personally going out into the fog with her knife to kill the alien.
* BlueBlood: Lord Palmerdale and company. The Doctor bottles up his contempt for them.
* ClosedCircle
* CueTheSun: The story ends while dawn is breaking.
* DeathByMaterialism: The last surviving non-regular character, Skinsale, is killed after his greed gets the better of him and he scrabbles for the diamonds that the Doctor had thrown away (only needing the best one to focus a laser). The Rutan gets him. It had been established earlier that greed was his FatalFlaw.
* DeathRay: The Doctor using his MacGyvering skills to weaponize the lighthouse beam into a sort of [[http://en.wikipedia.org/wiki/Archimedes#The_Archimedes_Heat_Ray Archimedes Heat Ray]] to blow the Rutan mothership into smithereens.
* DissonantSerenity: How the Doctor breaks the news of the lighthouse attack to Harker, Palmerdale, and Skinsale, complete with a [[CheshireCatGrin grin]]:
-->'''The Doctor:''' Gentlemen, I've got news for you. This lighthouse is under attack and by morning we might all be dead! Anyone interested?
* DoomyDoomsOfDoom: This episode was originally going to be called "Rocks of Doom."
* TheEdwardianEra
* ElectricJellyfish: The Rutan is pretty much a space version of this.
* EverybodysDeadDave: The Doctor and Leela are the only survivors, everyone else is massacred.
* FaceStealer: The Rutan dissects the first two lighthouse operators in order to learn enough human physiology to take the form of Reuben for the final two episodes. Later victims it just kills.
* {{Fainting}}: The '''Emotional Faint''', pulled by Adelaide on hearing of Lord Palmerdale's death.
* FogOfDoom: Caused by the Rutan scout trying to adapt the local environment to its own needs.
** OminousFog: For atmosphere.
* GetAHoldOfYourselfMan: Leela slapping Adelaide.
* InsignificantLittleBluePlanet: The Doctor is quite surprised by the Rutan's interest in Earth. It turns out to be fairly mild.
-->'''The Doctor:''' Why invade an obscure planet like Earth? It's of no value to you.
-->'''Rutan:''' The planet is obscure, but its strategic position is sound.
* {{Inspired By}}/{{Very Loosely Based On A True Story}}: The [[http://en.wikipedia.org/wiki/Flannan_Isle Flannan Isles]] mystery proved the inspiration for this adventure. The poem is even quoted by The Doctor.
* JerkAss: Lord Palmerdale.
* KillEmAll: No one survives this one except for the Doctor and Leela.
* LighthousePoint: Where all the action takes place.
* {{Mineral MacGuffin}}
* TheRadioDiesFirst: Skinsale sabotages the wireless to thwart Palmerdale's schemes.
* RealLifeWritesThePlot: Companion Leela's eyes changed from brown to blue as a result of the Doctor's laser, but the ''real'' reason was that actor Louise Jameson had decided to stop wearing the painful brown contact lenses.
* ScreamingWoman: Adelaide... until Leela slaps her.
* SicklyGreenGlow: The Rutan.
* TheSiege: A "base under siege" story like many before it.
* {{Spoonerism}}: Leela consistently mangles technological terms, from "boiler pressure" to "Mognal Sigulator" (signal modulator).
** "Teshnician."
* TemporaryBlindness: Leela.
* VoluntaryShapeshifting: The Rutan, with great effort.
* TheXOfY
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[-"[[http://en.wikipedia.org/wiki/Max_Headroom_broadcast_signal_intrusion#WGN-TV Well, if you're wondering what happened, so am I.]]"-]