´Black Heart’ er en film om mentale efterveer. Den følger tre new yorkere, som hver især bestræber sig på at behandle et personligt tab. Den fjerde karakter er New York, som forsøger at komme sig efter 9/11-tragedien og det sår, som stadig eksisterer.
John synes det er lidt ensomt at bo alene med sin hamster, Pjoske. Han har derfor inviteret sin ungdomsflamme Birthe over til en bid mad. I aften mødes de for første gang siden ”dengang i Helsinge MC”. Birthes besøg går dog ikke helt som John har drømt om.
Nadim er en minoritetsetnisk mand med tjek på tilværelsen. Han vil dog på ingen måde associeres med de mennesker, der ligner ham, men ikke kan opføre sig ordentligt. På vej til sin søsters fødselsdag sætter hans egen fordomsfuldhed ham i en position, der får dramatiske konsekvenser for ham.
Kira is a single mother struggling to build a better relationship with her distant teenage daughter, Lina. One day, Kira has a bright idea that she believes could pave the way for a stronger bond between them. In her attempt to make the idea a reality, enticing shadows of the past start catching up with her.
After the death of their father, Sigurd wants to bury the hatchet and forgive his half siblings, Astrid and Jens, for how they treated him as kids. But this does not go as planned, as Astrid and Jens do not believe they've done anything that warrants forgiveness. Sigurd feels snubbed and realizes that what he actually wants is an apology but this demand only escalates an already tense situation and before long, they start to fall into old habits, revisiting childhood traumas.
The film takes place in a near-future, where earth has punished all adults for not taking properly care of our planet. We follow a group of kids, left all by themselves in a trashed world, living day by day and trying to avoid the unknown future. The kids put all their fear into hating the adults, but what will happen when one of the kids starts to become one?