Karol Kremer (Filip Pławiak) is a diving champion from a privileged family living in the 1960s Cracow. Poland is under communist rule, and times are dark and murky while the city is empty and uninviting. After winning a diving tournament, Karol and his teammates go to a local funfair to celebrate his success. On his way back he discovers the body of a murdered boy, presumably the newest victim of the Red Spider, a terrifying serial killer, prowling the streets of Cracow. Spotting a stranger leaving the fairground, Karol follows him and tries to get closer to the silent, mysterious man, whom he believes to be the infamous murderer.

The Red Spider, a Polish-Czech-Slovak co-production, is a story inspired by two characters, Lucjan Staniak (‘the Red Spider’), a fictional crime literature serial killer, and the real acts of serial murderer Karol Kot (later named the Cracow’s Vampire), who was one of the youngest serial killers ever and became a media celebrity in the 1960s.