October 1914: the destroyer Svea emerged from the Stockholm archipelago bearing south-south-east. On board was Lars Tobiasson-Svartman, a naval engineer charged with making depth soundings for the Swedish navy. He is obsessed with measurement and precision, instincts reflected in his comfortable but cold relationship with his wife. Close to where soundings are taken, Lars rows out to a barren reef, presumed uninhabited, and discovers a young woman there. Despite her almost feral appearance, Sara stirs something in him. The mission is a success and the Svea returns to Gothenburg. Lars, however, remains haunted by this chance encounter, and feels compelled to return...