In the late 1800s, retired timber-man Ephraim Winslow (Robert Pattinson) is sent on a boat to serve a contract job as a wickie for four weeks on an isolated island with a gassy elderly man named Thomas Wake (William Dafoe). On the first day of the job, Winslow notices that there is a hole in his cot. As he digs into it, he finds a small wooden figurine of a mermaid and stuffs it in his jacket. Wake is perceived by Winslow as a strange and superstitious fellow, going up to the top of the lighthouse at night and stripping nude. Winslow decides to shrug it off but is drawn towards the ocean. He sees floating tree stumps in the water along with a horrifying image of a mermaid in the deep. Then he wakes, revealing this to be a dream.Over the course of his stay, Winslow is allocated the more taxing jobs, refueling the light, stirring the oil barrack, carrying heavy gasoline containers, and disposing of the two men's chamber pots. As the weeks progress, Winslow becomes more and more curious as to Wake's obsession with the light. He constantly is encountered by a strange seagull that constantly seeks to annoy Winslow at every turn. Wake sees this and encourages Winslow at dinner to leave it alone because it's bad luck to kill a seagull. The weeks continue, and Winslow constantly retreats to the supply cabin to masturbate to the figurine of the mermaid, and like clockwork, he sees Wake up on the top level of the lighthouse bare naked. One night at dinner, the two decide to get to know each other. They finally introduce each other by name and discuss the previous wickie. Wake says that his previous keeper passed away shortly after losing his sanity. Winslow tells Wake about how he used to work up in the North but decided to change profession, and Wake asks if he was running away from something he did on the mainland, which Winslow quickly shrugs off. Winslow asks Wake why killing a seagull is a bad omen, and he explains that Seagulls are vessels for the souls of dead seamen, which Winslow also shrugs off.The day before Winslow is slated to leave, he notices a major jam in the oil barrack and goes to see what the fuss is about. He opens the chamber to see a dying seagull stuck inside. The other seagull who has been tormenting Winslow for the past month flies down to the oil barrack and attacks him. Winslow grabs the seagull and violently beats it to death against a rock. That afternoon, the winds finally stop, and Wake becomes paranoid that a storm is destined to attack the island, and therefore proposes that the two of them drown their sorrows in alcohol before the ferry comes tomorrow. They board up the windows, and the storm begins. As the night progresses and the two get drunker and drunker, Winslow asks to go up to the top level of the lighthouse, which leads to an argument between him and Wake. The next morning, the ferry is nowhere to be seen, and Winslow decides to continue with his morning routine. This is, however, cut short by a mysterious figure washing up on the shore. Winslow approaches the body, which appears to be a naked woman until he looks down and realizes that she is actually a mermaid. He runs back into the cottage to find Wake stating that the rations were impacted by the storm. Wake informs Winslow that they buried a secret stash of rations next to the lighthouse that they will need to get. The two dig up the giant crate, but it is revealed to only have more alcohol.Wake says it will likely take a longer time for the ferry to get here due to the storm. More nights progress and the two become closer as they drink more and continue to be at each other's throats. One night in the bedroom, Winslow, in a drunken stupor, harasses Wake and criticizes his cooking skills, leading Wake to verbally curse out Winslow, asking Neptune to strike him dead in a lengthy soliloquy. The days of the storm continue, and Winslow slowly begins to drink on his own, and he loses his composure and his concept of time. He sneaks up to the top level of the lighthouse but cannot enter without a key. As he gazes into the light, he begins to have visions of tentacles moving inside. Wake begins to psychologically manipulate Winslow until he reveals that his name is actually not Ephraim Winslow. He actually murdered a timber-man by that name and assumed his identity. Wake accuses Winslow of "spilling his beans," and later on, Winslow drunkenly breaks the mermaid figurine in half. Winslow has another vision of him pulling up a lobster cage from the depths of the sea, containing the severed head of Wake's previous Wickie. Eventually, Winslow can't take anymore and tries to kill Wake in his sleep to steal the key. This proves unsuccessful, and Winslow tries to leave. He pushes the lifeboat out of the cabin, but Wake sees this and uses an ax to destroy the boat. Wake chases Winslow into the cottage, but inside, Wake continues with more psychological manipulation, claiming that it was actually Winslow that chased Wake around the island with the ax. An undisclosed amount of time later, the two have another drunken party together, until the storm becomes so powerful that the waves crash through the windows and destroying the cottage.The next morning the two wakes in a flooded cottage and Winslow decides to pick up Wake's diary. Inside, he finds that Wake has decided not to pay Winslow for his services once the ferry comes to pick them up, leading to another argument. Wake finally reveals that he knows Winslow killed the seagull and brought bad omens upon the island. Winslow attacks Wake and starts envisioning him as different people: first as the real Ephraim Winslow, then as the mermaid, then as Poseidon himself. Enveloped in imaginary tentacles, he beats Wake into submission. He then ties a collar around Wake's neck and forces him to walk and act like a dog. He takes Wake over to the hole where they kept the crate of alcohol and covers Wake in the dirt until he passes out. Winslow uses this opportunity to steal the key off him and runs back into the cottage to find the cabinet. Wake, in a fit of rage, bursts into the cottage with the ax and hacks Winslow in the shoulder. Winslow overpowers Wake and impales Wake right in the head. Winslow then walks up to the top level of the lighthouse and finally sees what is inside the light. He is then overpowered by the brightness and begins to maniacally laugh until he slips and falls down the stairs all the way to the floor. The film ends with a final shot of Winslow lying naked on the rocks, seagulls picking at his insides.
Storyline
As the wavering cry of the foghorn fills the air, the taciturn former lumberjack, Ephraim Winslow, and the grizzled lighthouse keeper, Thomas Wake, set foot in a secluded and perpetually grey islet off the coast of late-19th-century New England. For the following four weeks of back-breaking work and unfavourable conditions, the tight-lipped men will have no one else for company except for each other, forced to endure irritating idiosyncrasies, bottled-up resentment, and burgeoning hatred. Then, amid bad omens, a furious and unending squall maroons the pale beacon's keepers in the already inhospitable volcanic rock, paving the way for a prolonged period of feral hunger; excruciating agony; manic isolation, and horrible booze-addled visions. Now, the eerie stranglehold of insanity tightens. Is there an escape from the wall-less prison of the mind? — Nick Riganas