The journal was a chronicle of Isabella's life, described by her as holding her thoughts and feelings on things others didn't care to hear. The journal chronicled her love and obession for Piero, how she allowed him to use her blood and part of her finger in the pigment of the painting he made of her and how Isabella murdered Piero in a jealous rage. The journal, the one item Isabella was allowed to keep in the convent she was sent to and in prison was sent back to her family upon her death with the last entry recording how Isabella's murder of Piero was considered so horrific, she was convicted of witchcraft at her trial and sentenced to burn at the stake.
In 2015, the journal arrived at St. Philomena's Church along with other items from the estate of Isabella's family that had found their way to a monastary in Tivoli and then were eventually sent on to St. Philomena's Church. While conversing with the ghost of Isabella, Sister Mathias was shown the journal and told of its significance. After coming to suspect Isabella of being the killer of several unfaithful men, Sister Mathias read the journal and learned of Piero's murder, confirming that Isabella had become a vengeful spirit murdering men who cheated on their wives or girlfriends. Sister Mathias shared the discovery with the Winchesters and due to the journal chronicling Isabella's fate as being sentenced to burn at the stake for her crimes, Dean suspects that she is tied to the journal and orders Sam to burn it over his and Sister Mathias' protests. Before burning the journal, Sam reads it and finds the entry chronicling Isabella lending her blood and part of her finger to Piero's painting. This journal entry causes Sam to realize Isabella is tied to her painting and by salting and burning the painting, he is able to destroy her. It is unknown what happens to the journal afterwards, if Sam destroys it or not.
- The journal is written in Latin as shown when Sister Mathias reads from it.