Ever Dark Academy, Volume 6 by X. Aratare

At the Kaly party, Grayson discovers that his mother is in danger on Earth. But when he and his fellow Immortals attempt to save her, their plans go very wrong. Grayson mis-teleports to the past, still in his weak human body, where most of the Immortals are dead and Eyros is not a friend.

Ryder and the others try to get back to Grayson, only to find out that they have also mis-teleported to the past. A hostile Kaly slice awaits with an army of undead, determined to alter the future. Like Grayson, the Immortals are outmatched… but if they work together, they may have a chance.