Cal's been working on an elaborate spell to open a portal between universes and, after weeks of work and calculations to draft out the diagram and get all the symbols right and acquire all the right powders and pigments, he's eager to actually try it. Master Aubrey wants him to wait, but Cal has a day off today, and he doesn't see why the fact that it's Halloween should make any difference. He takes advantage of Aubrey's absence to go ahead on his own. After all, this is only practice, opening a portal to an empty, pocket universe. Even if something goes wrong, how bad could it be?
Famous last words.
OMG, there's usually a reason why Aubrey wants Cal to do certain things, or not do them, or wait to do them, even if he doesn't explain. And Cal will last a lot longer if he pays attention.
Opening the portal on Halloween was one of those things, but does Cal listen? No he does not! After a substantial amount of technical spellcasting Cal opens a gate to some otherwhere -- and he can't quite get himself back. And then he's got to convince a worried Aubrey that he's there at all.
This does lead to one of the more unusual sex scenes I've ever encountered -- it's cute and effective, though hotter for them than the reader.
Cal spends a lot of this story alone, first getting into mischief and then working out the scope of his difficulties. When Aubrey does come on the scene, the depth of affection comes out, as he establishes what's happened. The balance of power in a master/student relationship shows here, so does the love of partners.
This was a fun little bite of the Hidden Magic universe, but not a full meal in itself; read it after the novel and the other shorts. And definitely read those -- this is a great series.