1. The Floating City. The nations of the earth were stunned when a ship the size of a major city descended from beyond and started to hover above the Pacific Ocean. People everywhere tried to communicate with the ship, but they were ignored. A few tried to attack it, but their weapons were deflected by a powerful shield. While this was the first time humans had seen an alien ship, it was not first contact. 25 years ago, 200 of the aliens were sent to earth as babies, to be raised as humans and experience human life without any idea who they really were. Now that the ship has arrived, these aliens have been activated. Each one is recalled back to the ship and a computer uplink is used to teach them everything they need to know about their race and their technology.
When the 200 aliens return to the ship, 200 humans vanish without a trace. Each of these humans is someone one of the aliens desired in his or her previous life but never was really close with. It might be a celebrity they found attractive, a crush, or just someone they found attractive. These humans are to serve as a test to see if life on earth has made the aliens weak and unable to be part of culture on the floating city. Each human is given to the alien who desired them as a slave. Owning a human is a status symbol, but owning a well trained one is much more telling. Those who can master their human will be welcomed back to society. Those who cannot will lose their birthright.
The same uplink technology that allowed the aliens to learn about life on the ship can be used to create "triggers" in their new slave, things their master finds desirable. For example, one word might leave the slave unable to move at all, while another might leave them unable to speak for a time. A slave might be conditioned to feel cold or frightened if she gets too far away from her master. Specific triggers would need to be worked out, but there is a lot of room for creativity there.
2. Club Obsession. The newest nightclub, Obsession, opened a few months ago and has made quite a splash. Getting into the place is difficult, and getting into the VIP section is even more so. Lately, authorities have noticed that some of the people who make it into the VIP section are acting strange. They come out experiencing a euphoric high, but it quickly starts to fade. As it fades, the victim starts to go through serious withdrawl symptoms, but the symptoms don't get better. The condition just keeps getting worse, while the victim insists that she needs to get back into the VIP lounge. She doesn't remember anything that happened, but she knows that getting in will fix everything. The problem is that nobody ever gets into the VIP lounge twice. Tox screens on the victims come back negative, but the police are certain something is up. They have sent an attractive young officer undercover with instructions to get invited to the VIP lounge and see what is happening.
The truth is unlike anything the young woman could imagine. There are no drugs. The club is owned by a being who looks like a handsome young man, but is actually a very old and powerful entity who feeds on the emotions of others. To do this, he generates a euphoric effect in his prey so that he can take in some of that bliss and sustain himself. The bliss lasts for a few hours and then the victim crashes. They don't remember what happened, but they know they need more of what they had. The more time goes by, the more they would do anything for just a taste of what they had. The creature never feeds on the same person twice though, preferring fresh meals regularly. The undercover officer attracts his attention and he feeds on her. He isn't surprised when she tries to get back in looking for more, but he is surprised by her skills and strength. Perhaps there is value in keeping a human as a servant and slave, a regular source of nourishment in addition to what he takes in from the club.