Before this excerpt Herodotus is talking about how Darius became King of Persia with the help of the other six conspirators during their revolt against the Magus. In this aside he finishes off by showing why a brother could be dearer than a son or husband.
Of the seven men who revolted against the Magus, one, Intaphrenes, got his death through his own violence immediately after the rebellion. He wanted to enter the palace and speak with the king; and in fact the law was, that the rebels against the Magus could come into the king’s presence unannounced, if the king were not having intercourse with one of his wives.  Intaphrenes, as one of the seven, claimed his right to enter unannounced; but the gatekeeper and the messenger forbade him, telling him that the king was having intercourse with one of his wives. Intaphrenes thought that they were lying; drawing his scimitar he cut off their noses and ears, then strung these on his horse’s bridle and hung it around the men’s necks, and so let them go. 119.
They showed themselves to the king and told him why they had been treated so. Darius, fearing that the six had done this by common consent, sent for each and asked his opinion, whether they approved what had been done;  and being assured that they had no part in it, he seized Intaphrenes with his sons and all his household—for he strongly suspected that the man was plotting a rebellion with his kinsmen—and imprisoned them with the intention of putting them to death.  Then Intaphrenes’ wife began coming to the palace gates, weeping and lamenting; and by continuing to do this same thing she persuaded Darius to pity her; and he sent a messenger to tell her, “Woman, King Darius will allow one of your imprisoned relatives to survive, whomever you prefer of them all.”  After considering she answered, “If indeed the king gives me the life of one, I chose from them all my brother.”  Darius was astonished when he heard her answer, and sent someone who asked her: “Woman, the king asks you with what in mind you abandon your husband and your children and choose to save the life of your brother, who is less close to you than your children and less dear than your husband?”  “O King,” she answered, “I may have another husband, if a god is willing, and other children, if I lose these; but since my father and mother are no longer living, there is no way that I can have another brother; I said what I did with that in mind.”  Darius thought that the woman answered well, and for her sake he released the one for whom she had asked, and the eldest of her sons as well; he put to death all the rest. Thus immediately perished one of the seven. 120.