Space Viking by H. Beam Piper

Vengeance is a strange human motivation -- it can drive a man to do things which he neither would nor could achieve without it. and because of that it lies behind some of the greatest sagas of human literature!

They stood together at the parapet, their arms about each other's waists, her head against his cheek. Behind, the broad leaved shrubbery gossiped softly with the wind, and from the lower main terrace came music and laughing voices. The city of Wardshaven spread in front of them, white buildings rising from the wide spaces of green treetops, under a shimmer of sun-reflecting aircars above. Far away, the mountains were violet in the afternoon haze, and the huge red sun hung in a sky as yellow as a ripe peach.