Complex sentence: Lee Jang-ho (Ma Dong-seok), once a hotshot journalist, now a washed-up web newscaster, engages in search of conclusive evidence to prove the guilt of the perpetrators: the actress' diary.
Split into simpler sentences: Lee Jang-ho (Ma Dong-seok), once a hotshot journalist, is now a washed-up web newscaster. He engages in search of conclusive evidence to prove the guilt of the perpetrators--the actress' diary.