Of all the students at Umbrum Hall, Mary's one of the rarer types of magic user—a Gatemaker. She's able to jump from one place to the next and sometimes to carry others with her. That's instinctive. Now she's learning to do the heavy lifting, making gates that other people can walk through by themselves. Gates between places, and gates between realms.
That's a skill that will take years to master, but she may be running out of time.
Because Umbrum Hall is more than just a school; it's a sliver of reality that connects the elvish realm to the human world. Some people think the connections between those worlds are dangerous... and Mary's about to learn what they're willing to do to make their point.