Lee Wan and Shin Ki Tae were best friends in school, but Lee Wan harbored romantic feelings for Shin Ki Tae and confessed them, causing the two to part on unhappy terms. Seven years later, they're both navigating the job market, with Shin Ki Tae working as a programming ace at a gaming startup and Lee Wan pursuing his passion for illustration. When Shin Ki Tae's company starts looking for an illustrator for a new dating-themed game, Lee Wan applies for the job, raising the possibility of a second chance at romance.

“Dear.M” will tell the story of the campus-wide search for the mysterious “M,” an individual who is mentioned in an anonymous post on a Seoyeon University online community. The realistic romance drama will follow the changing relationships and budding romances between various characters in the wake of all the buzz about “M.” Ma Joo-A is a 2nd year student in the Business Administration Department at Seoyeon University. She has a warm heart and bright personality. She is not interested in pursuing a dream or having a romantic relationship. She has never had a boyfriend before. Cha Min-Ho is a 2nd year student in the Computer Science Department at Seoyeon University. He has a talent for developing apps with innovative ideas. He has been friends with Ma Joo-A for 12 years. Seo Ji-Min is a student in the Economics Department at Seoyeon University. She is also a member of the schools cheering squad.