It's 1910, and Theodulf Sauer has finally achieved a position befitting his ego: master lighthouse keeper at a newly commissioned station towering above Lake Superior. When his new wife, Willa, arrives on the first spring ferry, it's clear her life has taken the opposite turn: after being summoned home from college to Duluth when her father dies, she and her scheming mother find themselves destitute, and Willa is rushed into this ill-suited arranged marriage.

As the lighthouse station establishes, the new relationship teeters between tense and hostile. Willa takes solace in her fascination with the cosmos, especially in viewing Halley's Comet. Theodulf stands sentry over the lake, clinging to long-ago and faraway memories of happiness that fill him with longing and shame. Into this impasse, a clairvoyant girl and her resolute uncle emerge from across the cove. They see through the Sauers' façade and convey promise, sympathy, and insight that counter Willa's despair. Armed with renewed self-determination, Willa forges a path to happiness. But before she can grasp it, tragedy comes, and her future plunges toward a dark unknown.

A Lesser Light is a story about industry and calamity, science versus superstition, patriarchy's corrosive power—and the consequences when these forces collide in the wilderness of rapid social change.