Sisters of Quiet Mercy was a home created for troubled youths and parentless children. There, disenfranchised teens would supposedly learn such virtues as discipline and respect; all while enjoying lives of quiet reflection and servitude. Over the years, however, it became an abusive prison-like establishment run by the corrupt 'Sisters'.
Back in the founding days of Riverdale, the nunnery that would later be known as the Sisters of Quiet Mercy helped the townsfolk to find young girls to sacrifice for the Maple Harvest. It was during a time of dark arts and alleged witchcraft, so it was easy for the people to find girls to sacrifice.
In the early years of the establishment, the Sisters designed an exercise creating a fantasy world for the patients designed to instill terror to control them. Although it quickly got out of hand, they pursued it ultimately by creating Gryphons and Gargoyles, a game 'born of madness'.
During Prohibition, the Sisters ran a distillery in the basement and used to smuggle booze out to Sweetwater River via a tunnel running under the facility. The tunnel was also used by gay boys admitted to the facility's program to sneak out and to hook-up with other young men in Fox Forest. 
The Sisters helped cover up the assumed murder of a man who had killed Mr. Svenson's family and later the fact that the man killed may not have been the actual killer.
As a child, Penelope Blossom was raised by the Sisters of Quiet Mercy and was taught by Sister Woodhouse everything she knows about poisons. At a young age, she was given up for adoption to the Blossoms to be a young Clifford Blossom's sister and a child bride. It is unclear how much of their plan if any, the sisters knew about.
During her high school years, Alice Smith admitted herself to the facility to quietly give birth to her baby boy who was later given up for adoption.  Years later, when Alice's eldest daughter, Polly, became pregnant, she sent her to the home to give her baby up as well. However, Polly had no intention of doing so and ran away a few months later.  Polly confided in her sister Betty that she had been treated brutally there, a fact Betty threatened to unleash to the public if the Sisters did not give her the information she required.
In 2018, the Sisters of Quiet Mercy was one of the few places in the country that still did conversion therapy, although off the books due to it being an abhorrent practice and illegal in most jurisdictions. These patients were forcibly injected with chemicals, made to do brutal manual labour, beaten and forced to watch disturbing anti-gay videos. Cheryl Blossom was admitted into the group-home by her mother, Penelope and uncle, Claudius who claimed that Cheryl started exhibiting strange, deviant behavior and was mentally ill.  However, Toni and Veronica, aided by Kevin, sneaked inside the facility and helped her escape through the "gay hook-up tunnel." This was later sealed up with bricks.
The Sisters make a deal with Hiram Lodge allowing him to use their patients as test subjects in exchange for money. He supplies the sisters with Fizzle Rocks which they forcibly give their inmates. The fizzle rocks make the girls hallucinate that a statue of a large gargoyle in the basement is the fictitious Gargoyle King and terrify them into a brainwashed obedience.
The Sisters are arrested shortly after Betty and Ethel's escape from the asylum. They initially take a vow of silence to avoid charges, but Betty finds a loophole in unveiling that the Sisters have not truly worshipped any recognized God in decades. Once released on bail by an anonymous donor - presumably, Hiram - the Sisters were found dead within the facility seemingly having committed suicide via cyanide poisoning.It was later uncovered that Sister Woodhouse was alive and that she had killed the other Sisters.
- "Chapter Sixty-Five: In Treatment" (mentioned)
- Filming of the institute took place at a real mental hospital in Canada called Riverside.
- The exterior of the hospital was also used as the facade of another mental institution on the Lifetime TV series, Witches of East End, in which Mädchen Amick also starred.
Season 1 Screencaps
Season 2 Screencaps