They say unhealthy attachments are the root of most problems. Kim Luna knows this because she's attached to many things - her toxic ex-boyfriend, her kind but unavailable psychiatrist, and most of all, her opulent lifestyle that she lost after her family went into debt. So when she meets Moon Sung-hyun while working as a girlfriend-for-hire, it's no surprise that another unhealthy relationship begins between them... except this one may have deeply troubling consequences. Not only does Sung-hyun live in the very apartment Luna was kicked out of, but unbeknownst to them, there's something more sinister connecting their two families. Despite this, Luna's feelings for Sung-hyun grow increasingly sincere. Will Luna be able to stop her unhealthy habits and find genuine love with Sung-hyun, or will she become enmeshed in something much more poisonous?