Marie's job as a museum guard at the National Gallery in London offers her the life she always wanted, one of invisibility and quiet contemplation. But amid the hushed corridors surge currents of history and violence, paintings whose power belie their own fragility. There also lingers the legacy of her great-grandfather Ted, the warder who slipped and fell moments before reaching the suffragette Mary Richardson as she took a blade to one of the gallery's masterpieces on the eve of the First World War. After nine years there, Marie begins to feel the tug of restlessness. A decisive change comes in the form of a winter trip to Paris, where, with the arrival of an uninvited guest and an unexpected encounter, her carefully contained world is torn apart.