A classic of the fantasy genre.
The parliament of Erl comes to their Lord -- they want a magic lord. So the lord, obediently, sends his son off to find the title daughter. He succeeds. And this book goes on to chronicle what happens after.
It involves the ceremony of marriage for mermaids who forsake the sea, a dove cote, a hunt for the unicorn, the horns of elfland, a sword made of thunderbolt iron, and more, but the real reason for reading Dunsany is, of course, the crystalline singing prose:
To those who may have wisely kept their fancies within the boundary of the fields we know it is difficult for me to tell of the land to which Alveric had come, so that in their minds they can see that plain with its scattered trees and far off the dark wood out of which the palace of Elfland lifted those glittering spires, and above them and beyond them that serene range of mountains whose pinnacles took no colour from any light we see. Yet it is for this very purpose that our fancies travel far, and if my reader through fault of mine fail to picture the peaks of Elfland my fancy had better have stayed in the fields we know. Know then that in Elfland are colours more deep than are in our fields, and the very air there glows with so deep a lucency that all things seen there have something of the look of our trees and flowers in June reflected in water. And the colour of Elfland, of which I despaired to tell, may yet be told, for we have hints of it here; the deep blue of the night in Summer just as the gloaming has gone, the pale blue of Venus flooding the evening with light, the deeps of lakes in the twilight, all these are hints of that colour. And while our sunflowers carefully turned to the sun, some forefather of the rhododendrons must have turned a little towards Elfland, so that some of that glory dwells with them to this day.