Four old school friends have a pact: to meet up every year in the small town in Puglia they grew up in. Art, the charismatic leader of the group and creator of the pact, insists that the agreement must remain unshakable and enduring. But this year, he never shows up. A visit to his house increases the friends' worry; Art is farming marijuana. In Southern Italy doing that kind of thing can be very dangerous. They can't go to the Carabinieri so must make enquiries of their own. This is how they come across the rumours about Art; bizarre and unbelievable rumours that he miraculously cured the local mafia boss's daughter of terminal leukaemia. And among the chaos of his house, they find a document written by Art, The Book of Hidden Things, that promises to reveal dark secrets and wonders beyond anything previously known.