Jeon Jungkook is a Guardian of Red String. His job is to tie a red string of fate to two people’s pinky fingers. The two people are soulmates. He decides which person is the most compatible to other person. He makes no mistake. Sometimes he feels lonely because no one, but the Guardians, can see him. No human beings can see Guardians of Red String. That’s until he meets Kim Haerin. Kim Haerin was just a normal woman who works as a doctor until the accident that almost costs her life.

Shim Aejin is a music composer. Despite her young age, she is well known around Korea. Park Chanyeol is a pianist. Behind his cold facade, lies a sweet, charming, and also childish personality.

Hwang Haenim dan Oh Sehun harus bekerjasama dalam misi mereka untuk mengungkap kebenaran dibalik kematian mantan pacar Sehun, Choi Dalnim. Perasaan cinta mulai tumbuh diantara mereka. Dapatkah mereka mengungkap kebenaran dibalik kematian Dalnim? Dan yang lebih parah, pembunuh Dalnim sekarang mengincar Haenim. Mampukah Sehun melindungi Haenim dari tangan orang yang telah membunuh gadis yang dulu ia cintai? Atau akankah Haenim berakhir sama seperti Dalnim?