From the publisher's website:

The night covers the gloomy alleys with a veil of darkness. Jack is moving in the shadows... The finest investigators of the gaslight age have gathered The goal of the player who plays "Jack" is to escape the investigator before dawn or to leave the district by taking advantage of the darkness. For the player who is "the detective", his goal is to uncover which investigator Jack is impersonating and to catch him before dawn Eight investigators have gathered to catch the cunning Jack. But Jack is in fact cleverly impersonating one of them. By moving each character into light or shadow, the detective player makes successive deductions to uncover which investigator is in fact Jack, then he/she must try to catch the infamous Jack. The opponent, playing Jack, must do his best to delay the investigation. He can even try to use the darkness to secretly flee the district!