Bolzano, Tirolo meridionale. Parte dell'Italia, ma qui molti parlano tedesco. È una città dai due volti, con i cittadini di origine tedesca e quegli italiani, tutti ugualmente scossi quando uno spietato serial killer ritorna.
Prisma esplora le relazioni e identità di Andrea e Marco, fratelli gemelli, uguali esteriormente, ma diversissimi nel loro approccio alla vita, e racconta il loro gruppo di amici, uniti nella ricerca del proprio posto nel mondo.
Anna si è trasferita a Calura, un villaggio immaginario dell'Aspromonte e sua città natale, dove la sua amica d'infanzia Emilia prende il posto di sindaco. Quest'ultima sceglie la stessa Anna per la carica di vicesindaco.
The three young people react differently to the same challenges of survival, each on a different front line where everyone is a soldier. Things change, however, when fate brings Maria and Salvatore together.
A man is killed during the celebrations for the victory of the local hockey team. The investigation is entrusted to the public prosecutor Eva Kofler, supported by inspector Paolo Costa.
Despite their differences in character, Kofler and Costa understand that they must team up and look for new clues to solve the case. The investigation puts a strain on Paolo's love life, while Eva is worried about her father's illness.
As the relationship between Paolo and Eva becomes personal and the investigation into the crimes of is enriched with new elements, the theft of a painting sees among the suspects a painter friend of Kofler.
The discovery of the body of the owner of the stolen painting complicates the situation of Mathilde, the young painter. Searching the archives, Eva and Paolo find a lead for the first murder.
Costa and Kofler move on separate tracks: Paolo continues to follow the first case, while Eva must deal with a case that undermines the balance between the Italian and German communities.
As Eva gets closer to solving Matteo's case, she finds herself having to deal with a deep crisis with her husband Andreas. Paolo, meanwhile, makes some important discoveries about the "monster".
One step away from solving the case, Eva and Paolo are diverted to the murder of a researcher. Like her colleague, Costa, who finally gets reinstated in the ranks of the judicial police, is experiencing a moment of sentimental crisis.
Back to investigate the Monster, Eva and Paolo, closer than ever, put all the pieces together and begin to suspect that someone very close to them is hiding behind the killer.
