Puzzle

Debris II

Debris II starts with a meeting of police officers at the station: Frank, Pit and Nicole. At the meeting, Frank explains everything about a new kidnapping case involving four boys between the ages of 11 and 13. Apparently, the madman who committed this crime has sent a personalized invitation to Frank to go with other two people to an abandoned theater, where, according to the invitation, the play "Kidnapping of a Hummingbird" will begin at 23:00. The dark adventure of Frank, Pit and Nicole begins. What are the kidnapper's motivations? Why did they send the invitation to Frank expressly?