It is 1903. Thomas Edgar, a passionate collector of butterflies, is offered the chance of a lifetime: to travel to the Amazon as part of a scientific expedition. Hoping to find the mythical butterfly that will make his name and immortalise that of his wife, Sophie—for if he finds it, he will call it the "Papilio Sophia"—he eagerly accepts the invitation, and embarks on a journey that will take him to a whole new world.
On his return, Sophie greets her husband at the railway station, and is appalled by the change in him: he is thin, obviously sick, and apparently so traumatised by what he witnessed while he was away, he has been rendered mute. As Thomas struggles to find the words to describe what he's seen, it's unclear whether or not Sophie—and their marriage—will be able to withstand what he has to tell her, for the story that unfolds, the story behind Thomas's silence, is one of great brutality. Like the butterflies Thomas is so obsessed by, the butterflies that he catches and kills, it's a story of men who have been dazzled by surface splendour and wealth, and consequently refuse to acknowledge its underlying cruelty. But when that cruelty ends in murder, the question for Thomas—and Sophie—is whether or not he should be the one to speak out.