Irish fairy and folklore there were in abundance but there was no book of ghosts.

Suddenly a brilliant thought struck me. I wrote out a letter, stating exactly what I wanted and what I did not want and requesting the readers of it either to forward me ghost stories or else to put me in the way of getting them: this letter was sent to the principal Irish newspapers on October 27 and published on October 29 and following days. On October 30, the first answers reached me. Within a fortnight I had sufficient material to make a book; within a month I had so much material that I could pick and choose -- and more was promised.