On a Friday morning in a modest office block in eastern Paris, Bastien Cazenave is huddled with colleagues behind a computer screen. They are putting the finishing touches to the latest episode in his young company’s online murder-mystery game.

There is an air of quiet intensity as Pretty Simple Games releases its weekly instalment of Criminal Case, a sleuthing game that has rocketed up the social gaming charts this year. It is now the second most-played game on Facebook after King.com’s Candy Crush, overtaking those of Zynga, the biggest maker of Facebook games.

Criminal Case, the third game by Pretty Simple, has made the three-year-old company a global star of France’s start-up scene at a time when the country more often draws attention for the perceived business-unfriendly actions of its socialist government. Released in December, the game achieved 9.5m active daily users around the world in June. Mr Cazenave and his founding partner Corentin Raux say it will exceed €10m in revenues this year. “The margins are huge,” says Mr Cazenave. The founders expect to double their staff to more than 80 next year.