Joseph Aichelbaum's job is putting up posters in the Paris metro. Passengers hurry past his stepladder without a second glance. But there's one young woman who always stops to watch him work. One day, he finally finds the courage to approach her when, suddenly, a pickpocket snatches her purse. She disappears into the crowd in pursuit. Joseph recovers the purse, but he doesn’t know how to contact her. When he finally tracks her down, he finds out she works for Metropolis, an advertising agency that buys poster space in the metro for its clients. Is it a coincidence or a sign from fate? For Joseph, this is the beginning of an extraordinary adventure…