Lovers "trilogy" and film debut
Kim first gained attention when her television drama Lovers in Paris became a major hit in the summer of 2004, with viewership ratings averaging 41.3% and a peak of 57.6% (#11 highest rated of all time). The cast and crew flew to France to film several scenes in Paris and Nice, igniting a trend among Korean dramas for overseas location shoots. A Cinderella-like story of a cheerful, ordinary girl who becomes the housekeeper of a cold and suave businessman, lead actors Park Shin-yang and Kim Jung-eun shared the Grand Prize ("Daesang") at the 2004 SBS Drama Awards. Then at the 2005 Baeksang Arts Awards, Lovers in Paris won the following awards: the Daesang, Best TV Actress for Kim Jung-eun, and Best TV Screenplay for Kim Eun-sook and Kang Eun-jung. It also became popular internationally, and Kim Jung-eun was named Best Actress at the 2005 Asian Television Awards.
Kim chose another European setting for her next drama, Lovers in Prague (2005). In a gender reversal, Jeon Do-yeon played a diplomat in Prague, Czech Republic, who falls in love with a police detective, played by Kim Joo-hyuk. Kim Eun-sook said she wanted to feature a romance in which the woman's social status is higher than her partner, and wanted to make the social difference between the two main characters as extreme as possible by also making the heroine the daughter of the president of South Korea. Kim added, "Although some might say it is another unrealistic story, a drama is a drama. I just want to make people enjoy the fantasy." Jeon won the Daesang at the 2005 SBS Drama Awards, and Kim Joo-hyuk won Best TV Actor at the 2006 Baeksang Arts Awards.
Kim tried her hand at writing for the big screen in the 2006 melodrama Fly High (also known as Loving is Okay). Directed by Kwak Ji-kyoon, it starred Ji Hyun-woo as a high school student who falls for a girl with a terminal illness (Im Jung-eun). The film was a critical and box office disappointment, and Kim soon returned to her milieu, television.
Despite overseas shoots in Hainan, China, the conclusion to Kim's loosely named "Lovers trilogy" was simply titled Lovers (2006–2007). Based on the Lee Man-hee stage play Turn Around and Leave (that also inspired the 1998 film A Promise), Kim again cast Kim Jung-eun, this time opposite Lee Seo-jin, as they played a plastic surgeon and a gangster entering into an unlikely romance. Though not as successful as its predecessors, Lovers recorded solid ratings in the high teens to low-20s.