|The Memento Box Mystery|
|Date Ended||1914, same day, nighttime|
|Location||Beelzebub's Skull, Lithuania|
|Light Novel||Volume V|
|Anime||Episodes 16, 17 and 18|
|Victims||Several train employees|
|Casualties and Losses||Flooding of the Beelzebub's Skull|
Train heading to the Old Masquerade indefinitely delayed
|Previous Case||Bloodstains in the Festival|
|Current Case||The Memento Box Mystery|
|Next Case||Demise of Saubrème's Blue Rose|
|Case Overview Index|
Brian Roscoe returns to the Beelzebub's Skull after his last visit ten years ago. On his return, he seeks a certain item called the Memento Box, an object he acquired from a "nameless village". However, the man who was rumored to have taken the object, a man named Jupiter Roget, is nowhere to be found, and he finds himself alongside traveling companion Cordelia Gallo in a race to find the "Memento Box".
Cordelia then decides to entrust the fate of the Memento Box to her daughter Victorique de Blois and a boy named Kazuya Kujo, hoping that the discovery of the Memento Box would be able to shield her from the biggest hardships she would face.