The Blood Phoenix 5: An Avengers: Assemble Fan-Fiction

Adelaide Lehnsherr wakes up to a cold world.
She doesn't know her own name, or where she comes from, or who she is.
She is now possessed by HYDRA.
They begin to experiment on her, giving her the prison name of SA-8431. She is trained to become a deadly assassin by both Russia's the Red Room and HYDRA. For months on end she endures torture and cruelty of all kinds. But before she can graduate from the Red Room and take her rightful place in HYDRA, she is rescued and recruited by the Strategic Homeland Intervention Espionage Logistics Division, better known as SHIELD. Recruited to find a magical cube and defeat an otherwordly enemy. She is soon caught up in the fight of her life, one that will change her forever and set her on a different path...