At the historic University of Salamanca, a serial killer known as "Tuno Negro" (dressed in the traditional black cape and attire of a university tuna minstrel) begins brutally murdering students. The killer targets students who pass their exams through cheating, academic fraud, or undeserved privilege rather than actual knowledge, using internet chat rooms and Latin riddles to announce his victims. Alex (Silke), an architecture student, works alongside police detective Victor (Fele Martínez) and professor Arantxa (Maribel Verdú) to solve the historical clues and unmask the killer before becoming the next target.