Chen Dongdong (the heroine) is an orphan. Fu's mother, who raised her since childhood, was unjustly imprisoned.
She met Yan Yi (the male protagonist) in order to help Fu's mother reverse the case. Yan Yi's mother accidentally fell off a cliff and died.
Chen Dongdong happened to meet Yan Yi's mother on the day she was killed. In exchange, the two decided to work together to overturn the case.
Mission: Crime will eventually be brought to justice