Caith mac Sliabhin, condemned by the Sidhe in "The Brothers" for committing patricide, wanders along the river Guagach, accompanied and tormented by Dubhain, a mischievous pooka. Their journey takes them to Gleann Fiain where a beast from the river chases Caith up a hill to an isolated cottage. The occupants, twins Ceannann and Firinne, let Caith and Dubhain in and allow them to spend the night. Unbeknown to Caith, the birth of the twins 21 years ago set in motion a sequence of events that damned Gleann Fiain and cast a shadow over Faery.