It was a confusing plan, because the last episode ended with Kai giving Josie a fighting chance at escaping the prison world.
Unfortunately for Kai, Necromancer was no longer interested in helping out Kai after learning that his plan would’ve prevented Josie and all that dark magic from returning.
Kai might’ve had the chance to escape and fight another day had The Necromancer sent a minion to free him from his chains.
She ended up breaking the clock and releasing all that dark energy into her body, and once she remembered Kai and learned he was at the academy, she went about using that power to send everybody back.