Innocent Thing (English title) / Thorn (literal title)(가시)is a April 10, 2014 Movie directed by Kim Tae-Gyun and produced by Kim Tae-Gyun South Korea.
Joon-Ki ( Jang Hyuk ) is a popular P.E. teacher at a girl's high school. He is married to Seo-Yeon ( Sun Woo-Sun ) who is expecting their first child imminently.
During swimming class, a student named Young-Eun ( Jo Bo-Ah ) climbs up to the highest diving platform and jumps into the swimming pool. Joon-Ki jumps into the water and saves her. Days later, Joon-Ki is leaving school on a rainy late afternoon and runs into Young-Eun who is completely drenched. Joon-Ki takes Young-Eun back into school to change clothes. They spend time together in a classroom, with Young-Eun behaving in an flirtatious manner. Soon, Joon-Ki's marriage to Seo-Yeon is threatened.