Four men with complicated love lives refuse to admit they're getting older, and attempt to prove that forty is the new thirty!

Kim Moo-Young has been a zombie for the past 2 years. To survive, he has mimicked the mannerisms of humans in a village. He then leaves for the city. There, Kim Moo-Young opens an office to work as a private detective. He does not remember anything before he became a zombie. He struggles to live with humans and to regain his past memory. Meanwhile, Kong Sun-Ji used to be a writer of a current affairs complaint program. A witness in a case, she was working on, was attacked by an unknown man. Due to that, she quit her job. She becomes involved with Kim Moo-Young and takes a part-time position at his private detective office.

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