The Hidden Dungeon Only I Can Enter (Manga) Vol. 4

Noir and Emma are headed to a massive dance party thrown by the Bourne family. But in the middle of the festivities, a mysterious figure calling himself the Phantom appears and steals the Bourne heirloom jewels. Even worse, the Phantom declares his intent to kidnap Emma, too! Has Noir trained in the hidden dungeon long enough to defend his childhood friend from a master thief?