Originally written by Fujimoto Hitomi in a light novel called "Mangaka Marina Series" and its first volume is also made into manga by Taniguchi Amu.
In the manga, the story started with Marina who is a manga artist, got a phone call from her friend in Paris saying that she found a paper with treasure map written on it in a book she found in Paris. While they were chatting on the phone, Marina heard her friend answer someone who was knocking on her door, following by the sound of her friend struggling and gun shots, then everything is silent.
Concerns over this issues, Marina goes to tell her friend's mom about this and learns from her friend's mom that she just got a phone call from the police officer in Paris that her friend just got killed. Upon learning that her friend's mother has to go to Paris over this issue, she volunteers to go there herself, and is determined to investigate her friend's dead there.