This is a roughly Regency-era romance, in an England where magic works, the Sorcerer Royal is an important figure, and the Society of Unnatural Philosophers is a major institution. I say "Regency era" because Cho wisely refrains from peopling this world with familiar, historic names, and it at least appears that this England has a reigning king, not a regency.
Zacharias Wythe, Sorcerer Royal, is laboring under a few handicaps. The first and most visible is that he is African, a manumitted slave that the previous Sorcerer Royal, Sir Stephen Wythe, purchased as an infant and raised as his adopted son. Not everyone in English society shares Sir Stephen and Lady Maria Wythe's open-mindedness. Compounding the problem is that Zacharias succeeded to the Sorcerer Royal's staff when Sir Stephen died late one night, with no witnesses other than Zacharias and his own familiar, the dragon Leofric. And no one has seen Leofric since.
Murder used to be the traditional means of acceding to the position of Sorcerer Royal, though it has been considered beyond the pale for several centuries.
With all this, Zacharias also has problems that would challenge any Sorcerer Royal. The Fairy Court has imposed a ban on summoning new familiars, and a familiar is essential for making the jump from thaumaturge to sorcerer. And England's levels of atmospheric magic are declining, while France and other rivals suffer under no such handicap.
Meanwhile, Prunella Gentleman, age nineteen, is finding her time at Mrs. Daubeney's school for young gentlewitches increasingly untenable. She knows nothing of her mother, except the very evident fact that she was not a European, and her father committed suicide when she was very young, leaving her in the care of Mrs. Daubeney, with money to cover her education through age eighteen. She has begun teaching the younger classes of students at the school, but she has considerable magical talent and skill, and the main purpose of this school is to teach girls not to do the magic that is considered far too dangerous for the delicate constitutions of mere females. When Prunella finds her father's valise, containing a diary, a silver orb, and most startlingly, what her cautious studies have taught her are familiars' eggs, she glimpses a way out of her constrained future.
I enjoyed both the character development and the world building here. There are holes, but overall I found the world building very satisfying. It's not a small thing that Cho recognizes that all this magic would make the world different than the one we know, and doesn't try to shoehorn in recognizable historical figures. Both Zacharias's and Prunella's problems are complex, challenging, and entertaining, and none of conflicts are created by plot-driven stupidity. When characters don't share information, it's because they have real reasons not to, and it's not at all clear they've made the wrong decision.
This is a fun, engaging, thoroughly enjoyable fantasy from a writer I've only recently discovered.
I received a free electronic galley from the publisher via Penguin's First to Read program.