The series focuses on the eponymous fictional webtoon entitled W, written and illustrated by its legendary author and illustrator Oh Seong-moo (Kim Eui-sung) which begins to take a life of its own, like a distinct reality. W became so famous in South Korea that even its printed versions became best-sellers there.
The storyline of the webtoon W starts with the younger years of its main character Kang Cheol (Lee Jong-suk), a handsome and intelligent boy who is also skilled in shooting. He becomes famous in South Korea for winning the 50-metre pistol shoot at the 2004 Athens Olympics. But this fame is interrupted when the unknown Murderer massacres his family, and he is erroneously accused of the crime.
Another villain, Han Cheol-ho (Park Won-sang), handles the case to gain political popularity, urging the court to impose the death penalty upon Kang Cheol. Despite Han Cheol-ho's efforts, Kang Cheol is deemed innocent of the crime. Depressed over losing his family, he attempts suicide over the Han River but stops himself. Instead, Kang Cheol chooses to search for the real killer instead and devotes his life to crime-fighting.
Ten years later, Kang Cheol has become a multimillionaire. He starts "Project W" in an effort to catch the real culprit behind his family's death; part of the project is his television broadcasting company dubbed "W," after the initials of the interrogatives "who" and "why" (hence, the title of the webtoon). One night, he receives a suspicious phone call and is severely injured by the same mysterious murderer on the rooftop of his penthouse. Then even stranger things happen when the illustrator's daughter Oh Yeon-joo (Han Hyo-joo) accidentally enters the webtoon world. The story turns on the question whether he will be able to have a happy ending.
