The heartbeats in your home. All your servitors, so loyal and helpful. Sheryl, too. Are you really going to wait until you turn on them? You can't stomach that. Strangers are one thing, but the people who you're living with- ruling, even- should be as safe as you can make them. You aren't willing to wait. Indeed, you should take other precautions.
You go downstairs, and call your earth spirit, then order it to make several chambers in the cave, sealed with plugs of stone with handles, but too heavy for a human to lift. And air holes.
Then you head to the city. It doesn't matter who you kill, really, but you head for the slums out of habit and act the innocent. The gangs are more heavily armed than you remember, but that hardly matters; three toughs, young enough to be reckless and old enough to be lustful, corner you in an alley. You take a couple knife slashes on your arms, but those vanish in moments as you greedily suck the blood from a slashed neck and bask in the ecstasy. Your tight grip on the black pearl only seems to heighten the sensation, giving you the ability to dwell on it more intently than ever, and you find yourself being drawn in, hardly able to keep from sinking your fangs into flesh.
You drain two of them dry and dispose of the bodies as easily as before. The last you carry, unconscious, to your cave. The earth spirit has to show you the entrance, the vegetation is so overgrown- instead of the cavernous opening you remember, it's a narrow chute hardly wide enough for you to drop through comfortably. The interior has been smoothed, obviously by magical means, and the entire place feels comfortable to you. Secure. The sprite and earth spirit did an excellent job.
More than secure enough for the youth, at any rate. You throw him in the prison that you had the earth spirit construct and drop the seal on it. He won't be getting out, and you'll know where to find someone next time you feel hungry.