In the late 19th century, a young man named Ephraim Winslow is contracted to work as a 'wickie' for four weeks on an isolated island off the New England coast. He is to assist the aging lighthouse keeper Thomas Wake. From the moment Ephraim sets foot on the bleak and windswept island, he is subjected to the harsh realities of the job and the even harsher demeanor of Wake, who enforces grueling toil and strict discipline. Wake's tyranny extends to the most sacred realm of lighthouse keeping: the lamp itself, which only he is allowed to tend, casting an enigmatic allure over Ephraim.

As the days pass, Ephraim battles not only with the relentless maintenance demands of the lighthouse and the capricious weather but also with supernatural hallucinations and his deteriorating mental state. He is plagued by eerie visions that disturb his nights and a growing suspicion about Wake's past and the true nature of their work. The isolation and the constant din of the foghorn wear down Ephraim's resilience, and the line between reality and delusion begins to blur. Strained camaraderie gives way to bitter antagonism as secrets unfold, and the men grapple with their sanity and each other, bound to the island's desolation and the relentless beacon of the lighthouse.