Current user rating: 89/100 (420 votes)
- Movie: The Clue (English title) / Fourth Period Murder Mystery (literal title)
- Revised romanization: 4Gyoshi Churi Yeongyeok
- Hangul: 4교시 추리영역
- Director: Lee Sang-Yong
- Writer: Shin Jae-Ho
- Producer: Seo Myung-Jin, Ku Jung-Hee
- Cinematographer: Moon Ho-Jin
- Release Date: August 13, 2009
- Runtime: 86 min.
- Genre: Thriller
- Distributor: Lotte Entertainment
- Language: Korean
- Country: South Korea
11:40 AM - During 4th period when all the students are in gym class, top student Jung-Hoon (Yoo Seung-Ho) walks into a classroom to find fellow classmate Tae-Gyu (Jo Sang-Keun) brutally murdered. Jung-Hoon and Tae-Gyu has had a history of disliking one another.
11:50 AM - Da-Jung (Kang So-Ra) walks into the same classroom and discovers Jung-Hoon with blood covering his clothes standing near the murdered body. Da-Jung is a mystery buff herself and loves to use her deductive reasoning. She realizes that Jung-Hoon is the prime suspect, but doesn't believe that he killed Tae-Gyu. There's only 40 minutes before next period, in which all the students will come into the classroom and also discover the dead body.
12:05 PM - Jung-Hoon and Da-Jung frantically search for the real killer before the next period starts. With Da-Jung using her deductive reasonings they get closer to finding the identity of the true killer. Jung-Hoon's best friend Do-Il (Kim Dong-Beom) then takes part in finding the killer. When the 40 minutes are almost up, they discover a shocking new fact to the case ...
- Filming began April, 2009.
- After 70%-80% of the film's shooting was completed, director Shin Dong-Yeob dropped out of the project due to conflicts with the production company "Sway Entertainment (스웨이엔터테인먼트)". The movie will now be directed by Lee Sang-Yong (previously directed TV commercials). Because of the shooting delay, actress Kim So-Eun then bowed out of the film and was replaced by newcomer Kang So-Ra, as well as the principle cinemtographer. 
- "The Clue" opened #11 at the South Korean box office for its opening weekend of August 14 -16, 2009. The movie sold 34,595 tickets, accounting for 1.1% of all tickets sold for its three day weekend.
Additional Cast Members:
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