Book 4. Spoilers ahead for the earlier ones!
Gaius brings Rachel, after a little contretemps, to Ouroboros Industries, where she learns interesting things, gets an unexpected honor, and meets with a second cousin who's suffered memory loss, up to her first lessons in mundane physics.
Back at school, life goes on. Vlad gives her a bracelet that lets her communicate with him and the rest of the inner circle. Nastasia and Zoe vanish -- and worse, then Nastasia comes back alone. And Siegfried and Nastasia are on the outs. A lecture about the history of Roanoke. An ogre with a charmed life. Ice-skating. Attacks during thunderstorms. And more discoveries about the nature of the world and the things that are hidden from the magical world. And many more complications.