In 1958, the Knight of Hell Abaddon took over the convent in order to convert it into a demon factory by stealing souls from people and then transforming them. One of these victims was Sister Mary Catherine, one of the convent's nuns. In her soulless state, Mary Catherine wrote on the walls of her room in blood, carved the crest of the Knights of Hell into the wall, murdered two people and then committed suicide by jumping from the bell tower.
Mary Catherine's actions drew the attention of the Men of Letters who suspected demonic possession. The Men of Letters sent initiates Henry Winchester and Josie Sands to investigate under the guise of being a priest a nun from the Office of the Inquisition. Possessing the convent's Mother Superior, Abaddon granted them permission to search Mary Catherine's room for clues guided by Sister Julia Wilkinson. In the room, the two discovered the Knights of Hell's crest carved into the wall.
That night, the demons running the convent took several people to the basement to remove their souls, including Julia when she spotted Abaddon dragging a victim down the stairs. When Julia was the only victim left, Henry and Josie burst in and exorcised two of the demons possessing the nuns. However, Abaddon proved immune to the exorcism. In the confrontation that followed, Abaddon possessed Josie instead, leaving Mother Superior dead or unconscious. The demon possessing Sister Agnes, the last demon left aside from Abaddon, played dead with orders to continue their work until Abaddon's return. Henry was fooled that they had won and the next day, Abaddon asked that the nuns keep everything quiet for the safety of all involved. Unaware of Josie's possession, the nuns agreed with Abaddon subtly threatening Julia, who had survived, with her statement.
Over the following years, Sister Agnes continued to use the convent as her base in stealing souls for Abaddon, completely undetected. Julia left the order shortly after the incident due to her shame over not saying anything to Henry about Abaddon possessing Josie. The convent was ultimately shut down at some point and left abandoned aside from Sister Agnes' operation.
In 2014, during Abaddon's war for control of Hell with Crowley, the operation at the convent became one of many all over the place. By this point, Sister Agnes was forced to work with a demon possessing handyman Mr. Richie to kidnap any victims she could find. The two used an old van owned by the convent to travel around the area kidnapping people.
One of Sister Agnes' victims ended up going home and brutally murdering her husband, drawing the attention of hunter Sam Winchester, Henry's grandson. Like the Men of Letters before him, Sam suspected that the incident was demonic possession, but met Julia who informed him of the events at the convent in 1958. After seeing the St. Bonaventure van parked next to a victim's car in a security photo and learning that the convent was on the outskirts of town and abandoned, Sam realized that the convent was the demons base of operations.
That night, Sam entered the convent where he found a shelf containing the souls of Sister Agnes' five most recent victims. Sam quickly killed Mr. Richie when he attacked and faced off with Sister Agnes who explained how Abaddon was plotting to transform the souls into demons for her war with Crowley. Sam used an exorcism to distract Sister Agnes before killing her with the demon-killing knife. With the demons gone, Sam released the souls from their containers, returning them to their owners.