A high school math teacher leads a dull life, going from his job to a café to see the woman he admires from afar and then home to his apartment.
Kim Suk Go (Ryoo Beung Bum) is brilliant in math but awkward in all other aspects of his life. The woman he secretly likes, Baek Hwa Sun (Lee Yo Won), also happens to live next door to his apartment with her niece, Yoon Ah (Kim Bo Ra).
But one day, Hwa Sun’s violent ex-husband tracks her down at the apartment and attacks her and Yoon Ah. Suk Go quietly listens to the scuffle going on next door and then finally decides to walk over and knock on the door.
When Suk Go learns that Hwa Sun has killed her ex-husband during the fracas, he decides to help her devise the perfect alibi for the crime. Although Hwa Sun is cleared of the crime thanks to Suk Go, something just doesn’t sit right with Detective Jo Min Bum (Jo Jin Woong).
When Min Bum realizes that Suk Go, a high school classmate, is the next-door neighbor, he decides to investigate Suk Go also.
What strange secrets will Min Bum uncover about the reclusive Suk Go?
“Perfect Number” is 2012 South Korean film directed by Bang Eun Jin. It is adapted from the 2005 novel The Devotion of Suspect X by Keigo Higashino.