Yeh Xin's (Tia Lee) life seems to be perfect: young, beautiful, top student specializing in criminal psychology, loving parents, and a charming boyfriend Lin Miao (Ray Chang) who is a forensics specialist. One day, Xin's father flies to the USA for a medical seminar. Then on one rainy night, her dog digs up a human bone in her backyard. Next, she receives a letter in the mail warning that her seemingly perfect life is about to collapse.

While the investigation going, Xin accidentally finds hundreds of letters written by a girl named Bugzy, in her boyfriend's study room. Suspecting being cheated and being jealous; Xin begins to read the letters. She then discovers that other than Zhihuan, two other girls are also accidentally died because of Xin's boyfriend. Xin finds herself entangled in a bizarre murder mystery. Moreover, she develops multiple personality disorder.

''When Geek Meets Serial Killer'' director Remus Kam adapts a 2007 novel by popular online writer Ye Congling into the suspense thriller ''The Perfect Girl''. ''When Geek Meets Serial Killer's lead actor Ray Chang stars again, this time opposite Taiwan television actress Tia Lee (Fall in Love with Me) as the heroine who finds out she's not so perfect after all.

人格分裂是介於精神病理學和心理學的一種病症，大多時間隱藏的主人格並不會出現，而自身也並不會發覺其實已經被其他人格所支配了。 葉欣（李毓芬飾）是專攻犯罪心理學的高材生，擁有美麗的外貌和與之媲美的聰慧頭腦，父親葉景孝（謝祖武飾）是心臟外科權威，男友林邈（張睿家飾）則是專長法醫學的年輕法醫，葉欣生活週遭的一切看起來是那麼的完美，但在某一天下大雨的深夜，葉欣舊家後院被闖入的野狗挖掘出人骨，同時葉欣收到署名罪惡小葉的信件，信中預告葉欣看似完美的生活即將面臨崩潰。 隨著罪惡小葉的倒數預告，葉欣的週遭牽扯出多條犯案手法離奇的兇殺命案，葉欣追尋線索同時發現男友與父親各自與命案有著牽扯不清的關聯性...葉欣是否能夠在這一切謎題中找到解答。