Del, the wizard's apprentice, has known for a while that he needs to make a decision, if he wants to live: run away, or kill his master. He didn't plan on companions.
There are transformations, brushes with myths, stories that turn out to be closer than skin. Del helps Kelsie and Nicholas, his master's stepchildren, to break away from a cruel spell, then to take their revenge; shares with them his magic. He doesn't expect them to stay. Friendship doesn't mean much when the people hunting you, who want to cut you into pieces, can whip a hurricane out of a gentle breeze, or craft barriers of searing pain. The twins have a soft life to go back to; he never did. He doesn't expect to come out of this alive.
This novella is part a dark version of a children's adventure, part fairytale, and both of those more than it's fantasy YA, though that's what it will probably be slotted into as genres go. It excels in telling without telling, letting us fill in a world with a history around details that come up as they become relevant.
The description of emotions is similarly constrained in places even as the stakes are high and losses, terrors and actions extreme as the kids are pushed to the limit of endurance. Del, whose point of view we follow, tries not to feel very much, since most of what seems available to him to feel is bad; and feeling something good might be potentially even worse, considering what he'd then have to lose. Until the very end I never even realized I was reading an emotional journey, aside from a story of developing friendship. It's when that bubble of misery broke, even just a little, that I saw it, and the difference was enormous.
The fantasy here is the act of leaving, of cutting free, and finding a home that isn't a place.