Sean Reilly is an artist who drove an ambulance in the Great War and now finds it impossible to paint. Challenged by Futurists to spread their political creed in Fiume, a city on the western coast of the Adriatic, he agrees to go, hoping it will restore his faith in the future.

Fiume has become a global sensation. Italy and Jugoslavia each lay claim to the strategically important port city. While the Paris Peace Conference debates Fiume's fate, a legion of Italian veterans has marched in and occupied it, installing the poet and war hero Gabriele D'Annunzio as Comandante. Sean is immediately dazzled by Fiume's wild festivals and unbridled promiscuity, and by D'Annunzio's plan for a multinational crusade for justice. He falls hard for a beguiling woman who takes photographs in every part of the city. They are exploring an old castle together when he chances upon a suspicious sight in the hills to the north.

Sean's obsession with what he has seen leads him into Fiume's dark side where bloody Fascist-instigated attacks terrorize the city's Croatian minority and Croat militants respond in kind. Confronted with a future unlike anything imagined in Futurist art, the troubled artist scrambles to unlock the secret in the hills that some people will go to any lengths to keep hidden.