It's Easter, 1872. Fires burn in St Petersburg, a prelude to the revolutionary turmoil that will shake Russia a generation later. As the springtime thaw begins, a body rises to the surface of the Winter Canal. Following an anonymous tip-off, magistrate Porfiry Petrovich is drawn into an investigation of the radical intellectuals who seek to fan the flames of revolution. In the meantime, junior magistrate Pavel Pavlovich Virginsky plays a dangerous game of his own.