Best known for his poetry, William Butler Yeats (1865-1939) was also a dedicated exponent of Irish folklore. Yeats took a particular interest in the tales' mythic and magical roots. The Celtic Twilight ventures into the eerie and puckish world of fairies, ghosts, and spirits. "This handful of dreams," as the author referred to it, first appeared in 1893, and its title refers to the pre-dawn hours, when the Druids performed their rituals. It...