Samhain Crossing

They recognize each other across twenty centuries. 

On the ancient Celtic feast day of Imbolc, a mysterious, but empty, box is discovered, built into a wall of a first century structure in the ruins of Carn Euny in Britain.  Itching for distraction, the dig team drop a note into the box, and the next morning find an answer written in ancient Latin. 
 
Dig director, Doctor Daria Caitini, declares the response a hoax, but when more and more letters arrive on each successive Celtic feast day, Daria finds herself drawn into corresponding with the writer, a first century druid called Cadfan, who is hunted by the Romans, and who recognizes her dedication to her work and her essential loneliness, too….