The story shows in a subtle way how 7 friends were involved in a murder and trial of their 8th friend.
In the last 30 minutes we know the truth: one psychopath/sociopath teenager manipulated his 7 friends to turn them into thieves, extortionists, etc.
And then, he killed the 8th friend "by mistake". So he devised a way to blame the best client of his wealthy family.
And he get away with it.
Review of Wij
