As this Korean drama opens we are introduced to Kim Sum, a school girl who has developed an artificial intelligence program called 'Someone'. She is approached by a woman working in the industry. A few years later she is working for the company and has developed an AI to use in a dating App called 'Somebody'. It soon becomes clear that the app is being used by Sung Yun-oh, a serial killer, to find his victims. Kim Sum and two of her friends; Yeong Gi-eun, a wheelchair bound police officer; and Im Mok-won, a shaman, find themselves caught up in Sung Yun-oh's activities... putting them in clear danger.
Fans of other K-dramas may think they know what they'll be getting but they are likely to be surprised; I certainly was. It is dark in tone and there are few laughs to be had... I can't recall the last time a series kept me on edge the way this did. Some may find certain scenes glacially slow but for me these served the raise the tension to almost unbearable levels. The main cast, which was small, did an impressive job. Kang Hae-lim impressed as Kim Sum and Kim Young-kwang excelled as Sung Yun-oh, making him genuinely frightening. There are several times when characters are in danger, sometimes for extended periods. There is also far more sex and nudity than one expects in Korean series. Overall I would certainly recommend this to anybody wanting a really gripping drama; it won't be for everybody though.
These comments are based on watching the series in Korean with English subtitles.