Three lighthouse keepers, Thomas, James, and Donald, embark on a six-week shift to the remote Flannan Isles. Upon their arrival, they find the island desolate and eerie, yet they settle into their routines quickly. While exploring the area, they come across an ordinary rowboat washed ashore with a chest inside it. Curiosity turns to greed when they discover that the chest contains gold bars. The isolated environment and newfound wealth brew tensions and distrust among the men, interrupting their once mundane existence.

As paranoia escalates, external threats from mysterious visitors compound the already tense atmosphere. The trio struggles to protect their fortune while grappling with the emotional and psychological strains of isolation and suspicion. Their bond deteriorates as secrets, fear, and guilt increasingly take hold over them. Balancing the perils of outside interference with their internal conflicts, their once straightforward mission evolves into a harrowing ordeal.