Inside the box were all Life Caskets.
Each one was only the size of a palm, forged entirely from mithril, and imbued with powerful defense magic, as well as filled with undead essence, making it impossible to differentiate them from the outside. Only by breaking the magic and opening the casket, could one confirm what exactly was inside.
This box of Life Caskets cost Amberser many Gold Coins; one could say that within the entire castle, the most valuable item was this box of Life Caskets.
Amberser casually picked one, sent it to Withered Rose via the Necromancy Codex, and then sent another message: "Lady Rose, please, my life is in your hands. This is our secret between us, please do not tell anyone."
"Withered Rose: Don't worry."
Amberser closed the Necromancy Codex with satisfaction, then grabbed Harvey, who had been immersed in reading books in his cell.