Broken but not defeated, he turns his focus on body runes with hopes to re-animate his assistant's body. Unfortunately, he was only able to generate enough 'body energy' to revive a single arm, which reacted by flailing violently and attacking the assistant itself; Vitruvius amputates the limb but vowed to re-arm his assistant one day. Make sure you've read the book, and use the soft clay on the ragged book to make a key mould. With the key mould in the inventory, use one elemental bar on the furnace to make a ragged elemental key.