The Daemon was initially trapped and found by members of the Order of the Blessed Inquiry. This divison of the Adepta Sororitas was not engaged in battle but instead sought to study the imprisioned Daemon in order to learn secrets that could be used to fight Chaos. This continued in secret for three hundred years where many members of the Order fell victim to the Daemon's lies.
Eventually, Asteroth was partially freed and he destroyed the convent which became a lost order within the Imperium. Taking the ruined bodies of seven hundred Sisters, the Keeper of Secrets stitched their forms and minds together into what it considered as a work of art. Their minds forged into a single construct that became known as the Screaming Cage; a large screaming sphere with the bones of the Order attached to it. As the Daemon sought to kill the few remaining Sisters, a young Ephrael Stern seemingly committed suicide. However, the Order of the Blessed Inquiry that resided within the Screaming Cage used what power they had to bring her back to life and filled her with great power to combat Chaos. Once returned, she was told to flee and the Sisters hid her presence from the forces of Chaos. Stern's memory of these events were erased but her unnatural power as a Daemonifuge made her the object of suspicion with many viewing her as a corrupt vessel of Chaos.
Later events led to Inquisitor Silas Hand taking Ephrael Stern and the Sisters of her new Order to the planet Parnis in order to investigate the findings of the lost order on the planet. The machinations of Chaos later resulted in their ship the Hammer of Thor crashing on the world. Later, Stern and her comrades discovered the Screaming Cage where the minds of the imprisoned sisters within revealed to Ephrael her past. They later transferred all the knowledge of Chaos that they possessed into Stern's mind so that she could use it to fight the denizens of the Warp. Ephrael later used some of this Warp power and empowered Silas Hand which he used to fight the Daemon Asteroth who was later forced to flee in order to escape destruction.
Stern later wrote down much of what she knew into the Stern Codex which contained a thesis that descrived the strengths and weaknesses of the Chaos God Slaanesh. She later recieved a dream vision from the dead Silas Hand that told her to take what she knew and place it within the Black Library of the Eldar race.