The Unseen Elder seems a trifle surprised you’re still alive, and is content to listen to you, if only for a moment, once you present your gift to him. When you’re ordered to speak, you can:
Concentrate on only the factual (yellow-colored) comments and questions; asking about Dettlaff. Explain the situation, choosing any (yellow-colored) conversation choice, but focus on explaining how Dettlaff will be a threat to the Elder; as the population currently under attack will seek out every last vampire to kill over the following decades, which could really hinder the Elder’s sleeping patterns. The Elder seems agreeable. Answer as you wish in regards to what you want to do with Dettlaff: The Elder agrees to summon Dettlaff to Tesham Mutna, once you reach this fortification yourself.
Asking optional questions infuriates the Elder; to such an extent that if you try this more than once, the Unseen Elder tires of you, and snuffs out your life. This isn’t the recommended way to end this chat.
Dismissed from the lair of the Unseen Elder, you reunite with Regis. Feel free to ask if all Unseen Elders are like the one you met, and how Regis can tell you the previous near-death experience went “better than expected” (answer any following questions as you wish). Then you tell Regis it is time to face Dettlaff.