Sister Mathias is the director of social services at St. Philomena's Church in Worcester, Massachusetts.
While working at St. Philomena's Church, Sister Mathias encountered many ghosts due to the burial crypts beneath the church and thought little of it due to her spiritual beliefs. Most were lost souls that eventually moved on on their own. Eventually, after Isabella's things were sent over from Italy, Sister Mathias met her and befriended the ghost, unaware that Isabella was actually a venegful spirit. Over the next three weeks, Sister Mathias learned of Isabella's sad history while unaware that Isabella was murdering unfaithful spouses.
In 2014, the church was visited by hunters Sam and Dean Winchester who were investigating Isabella's murders. Sister Mathias was assigned to aid them, but didn't make the connections between the murders and Isabella until she overheard the Winchesters discussing how a ghost was causing them. Realizing that Isabella arrived shortly before the murders began and knowing some of Isabella's tragic backstory, Sister Mathias read Isabella's journal and learned of her murder of Piero in revenge for him rejecting her and then going to another woman.
After realizing Isabella's guilt, Sister Mathias contacted the Winchesters and informed them of her discovery and her knowledge of the existence of ghosts. When the Winchesters tried to figure out how to dispatch Isabella since she was likely buried in Italy, Sister Mathias informed them that she'd discovered that Isabella had been convicted of witchcraft and sentenced to be burned at the stake from her journal, meaning there would be no body to burn. Figuring that Isabella is tied to her journal, Dean orders Sam to burn it while he and Sister Mathias search the church for Isabella. After finding the priest murdered by Isabella, Isabella possesses Sister Mathias to kill Dean. As the two struggle, Sam discovers that Isabella is tied to her painting and salts and burns it, expelling Isabella from Sister Mathias. Isabella pleads with Sister Mathias to help her as they are friends, but Sister Mathias just watches as Isabella goes up in flames.
Powers and Abilities
Although she never received any training in supernatural knowledge, due to the convent spiritual condition and her capability to adapted with it, at least she awakened her supernatural awareness.
- Mediumship - She capable to feel and aware about the presence of any supernatural things such as ghosts, poltergeists, and even various restless spirits in the convent. She also capable to directly contact them if needed. However she did it secretly.
- While helping solve the case, Sister Mathias showed knowledge of investigative techniques, impressing Dean greatly.
- Sister Mathias notes that she and Isabella have a lot in common including painful love lives. This, along with other comments Sister Mathias makes, suggests that some sort of bad relationship led to her becoming a nun to deal with the pain and find a higher purpose for herself to believe in to get over it.