This narrative poem is composed in three parts, and consists of a dialogue between the aged Irish hero OisÃn and St. Patrick.OisÃn relates his three-hundred year sojourn in the immortal isles of Faerie. In the isles, OisÃn married the beautiful Sidhe Niamh: together they traveled, feasted, and quested. At last OisÃn succumbs to the temptation to return and visit the lands of mortal men: inadvertently slipping from his faerie horse, his body touches the ground and instantly puts on the flesh of a decrepit old man.
OisÃn describes various islands and what he did there: contrasting his noble deeds with the degenerate weakness of the present generation.