After surviving Phyrexia and rebuilding a body inside the Meditation Realm, Jace discovers that survival has not made him whole. His mind fractures under its own damage and his answer is creation. Within a private fold of reality he shapes Tam from part of his soul, gives her a gorgon's form and calls her a person in progress rather than a finished tool.
Years later, Tam returns to Hexhaven after infiltrating the true Strixhaven and abducting Jadzi. The mission should prove her usefulness, yet the friends she betrayed remain present in imagined conversations. Hexhaven's rigid lessons and blank-eyed cadets cannot supply the belonging she briefly found on Arcavios.
The Theorist explains the hidden purpose. The Echoverse is attached to his body and is failing. Jadzi's oracle soul will return to the creation of Arcavios when she dies; by following it, he hopes to learn how two planes became one and use that structure to anchor his copy to the original Multiverse.