“Many a keeper’s lost their mind to quicksilver,” warns James (Gerard Butler) as Donald (Connor Swindells), his trainee lighthouse keeper, dabbles a gloved hand in a puddle of mercury. It’s 1938, and the men, accompanied by a veteran keeper named Thomas (Peter Mullan), have arrived for a 6-week shift on a barren lump of rock off the coast of Scotland. The mercury leak is only the first sign of the many troubles to come.

As it turns out, it will be gold, not silver, that turns their heads in “The Vanishing,” a middling good-guys-gone-bad thriller (and no relation to George Sluizer’s ingenious 1991 shocker). Inspired by the Flannan Isles mystery of 1900, when three keepers disappeared without trace, Joe Bone and Celyn Jones’s script takes pains to differentiate the three leads. Thomas is tired and reclusive, haunted by personal tragedy. James, by contrast, is a loving husband and father and a natural mentor to the volatile, inexperienced Donald.