SHH is the story of friendship being put to the test. On the night of a school party, four girlfriends are waiting to be questioned by the school's principal. The bond between the girls appears to be strong and unbreakable. One of them however seems to be under more pressure than the rest.

The story is centred on Lena, who is 38 years old and lives in Poland. One night, while driving to Łódź on a motorway, she witnesses an accident. She sees how a woman trapped in a car burns to death. The screams of Nina, the victim, haunt Lena from then on, and she starts to suffer more and more from insomnia. Lena tries to find out who the woman was. This quest whisks the protagonist away on a physical as well as an emotional journey into her subconscious. The nights on the motorway turn into nightmares, and Lena has to find a way out of them.