1.

enigma
/ɪˈnɪɡmə,ɛˈnɪɡmə/
noun
a person or thing that is mysterious or difficult to understand.

In which a new environment leads Na Jieun to get tangled up with her mysterious seatmate, Kang Taehyun.

‣ book 2 of the 'Mafia' series.