Full presentation by Pretty Simple's co-founders Corentin Raux and Bastien Cazenave, on designing the virality and retention for the hit social game of investigation Criminal Case. Launched in November 2012, Criminal Case went from 0 to 9 million players in just 6 months, and reached #2 most played game on Facebook by May 2013. Only 2% of all players came from ads, which means a staggering 98% of players discovered and played Criminal Case organically. The popularity of Criminal Case rests in large part on the quality of the game itself, but though this presentation discusses our overall design choices briefly, how to design a good game is (way) beyond its scope. This presentation focuses on the key pillars of the success of Criminal Case: optimizing the first time user experience, designing virality and retention, and understanding their relationship. This presentation is supported by actual examples and numbers from Criminal Case.