"Momento Mori" is a Latin phrase meaning, "Be mindful of death" or, "Remember that you will die." In this game however, "Momento Mori" refers to a secret brotherhood knows as "Ikuinen Nukkuja," or "The Eternal Sleeper" in English. Their objective? To hide artwork away from the general public. When a priceless artifact is replaced with a perfect copy in the Hermitage Museum of St. Petersburg, Chief of Police Colonel Ostankovic believes Ikuinen Nukkuja is responsible. Ostankovic assigns the case to one Larisa Ivanovna Svetlova. Together with her friend, a reformed fence and counterfeiter Maxime Durand, the two will try to uncover the mystery behind Ikuinen Nukkuja and why they are so keen on hiding away painting after painting featuring the same topic – The Angel of Death.