A mad painter dies by suicide in a village in the Ferrara area, after having painted a terrible fresco, representing the martyrdom of San Sebastiano between two grinning figures. Those interested in the tourist development of the locality, considering the work of Buono Legnani an attraction, decide to restore the fresco and bring in their fellow citizen Stefano, a failed painter. The young man is haunted by strange and disturbing facts, while his friend Mazza, before disappearing with a fake suicide, reveals to him a fantastic story of which he is unable to give him the details. Before discovering the truth and risking his own life, the restorer witnesses the death of the sexton Livio, the taxi driver Coppola, his lover Francesca, a schoolteacher. Someone is sacrificing victims in memory of the deceased painter.