the continuing adventures of Rachel Griffin. Spoilers ahead for the earlier two.
It, in fact, opens with Rachel and her friends experimenting with the dream-walking powers from the earlier books.
This book takes up more time than the earlier ones, and progresses through several months as they learn more about the significances of the sacrifices. It includes a castle in Transylvania, a goose that's more than it seems, learning more about the princess's visions and what they mean about the characters' pasts (Gaius gets reassured about something he feared), a discussion of the sinking of the Titanic, ghosts and skeletons, the issues of studying history and science when the very universe can be changed, Vladimir's love, and more.
Plots are foiled, but there is clearly trouble ahead.