This is book number 2 in the Yellowstone series.
Ghosts. Ghosts? Ahem. GHOSTS.
The summer after riding shotgun on the nerdiest odyssey this side of the Pecos, plucky misanthrope Ryland Taggart finds herself on a Tuscan farm assisting her dangerously impractical botany professor investigate a rash of unexplained crop failures. They find more than they were prepared for when Ryland begins to get nightly visits from the ghost of 19th-century bandit-king, Domenico Tiburzi, pleading with her to save the land.
Si deve seguire il raggio verde, he implores. You must follow the green ray.
When she is given an 1883 edition of Jules Verne's The Green Ray accompanied by a photo of an unnamed woman, Ryland takes up Tiburzi's challenge and embarks on a cross-European quest to uncover the farm's mysterious past. But can she escape the ghosts at her heels--both the mostly dead kind and the phantoms woven from her own regrets--long enough to find how the farm's destiny is entwined with her own?