Defenders of the Realm
Dresdak is a mindflayer who the party found in the binding circle of Castle Tethyr, one of the few untouched rooms left.
He was researching the magics that bound the genies and offered the party to help complete the intended ritual and draw the essences of the genies into the castle defences. In exchange he only asked to continue his research and boarding within the castle.
Dresdak is not exactly sure what this gives the castle and that is his next topic of research, discovering what the spells exact purpose was.