Author's notes: The story is inspired chiefly by the passage in Unfinished Tales: Part III: The Third Age: II - Cirion and Eorl and the Friendship of Rohan and Gondor - (i) The Northmen and the Wainriders:
But at length, King Calimehtar, son of Narmacil II, being free from other dangers, determined to avenge the defeat of the Battle of the Plains. Messengers came to him from Marhwini warning him that the Wainriders were plotting to raid Calenardhon over the Undeeps; but they said also that a revolt of the Northmen who had been enslaved was being prepared and would burst into flame if the Wainriders became involved in war. Calimehtar therefore, as soon as he could, led an army out of Ithilien, taking care that its approach should be well known to the enemy. The Wainriders came down with all the strength that they could spare, and Calimehtar gave way before them, drawing them away from their homes. At length battle was joined upon the Dagorlad, and the result was long in doubt. But at its height horsemen that Calimehtar had sent over the Undeeps (left unguarded by the enemy) joined with a great Èored led by Marhwini assailed the Wainriders in flank and rear. The victory of Gondor was overwhelming - though not in the event decisive. When the enemy broke and were soon in disordered flight north towards their homes Calimehtar, wisely for his part, did not pursue them. They had left well nigh a third of their host dead to rot upon the Dagorlad among the bones of other and nobler battles of the past. But the horsemen of Marhwini harried the fugitives and inflicted great loss upon them in their long rout over the plains, until they were within far sight of Mirkwood. There they left them, taunting them: "Fly east not north, folk of Sauron! See, the homes you stole are in flames!" For there was a great smoke going up.This passage enlarges upon the information found in LotR's Appendix A: Annals of the Kings and Rulers:I - The Númenorean Kings: (iv) Gondor and the Heirs of Anarion
The revolt planned and assisted by Marhwini had indeed broken out; desperate outlaws coming out of the Forest had roused the slaves, and together had succeeded in burning many of the dwellings of the Wainriders, and their storehouses, and their fortified camps of wagons. But most of them had perished in the attempt; for they were ill-armed, and the enemy had not left their homes undefended: their youths and old men were aided by the younger women, who in that people were also trained in arms and fought fiercely in defence of their homes and their children. Thus in the end Marhwini was obliged to retire again to his land beside the Anduin, and the Northmen of his race never again returned to their former homes. Calimehtar withdrew to Gondor, which enjoyed for a time (from 1899 to 1944) a respite from war before the great assault in which the line of its kings came near to its end...
In the meanwhile the Wainriders licked their wounds, and plotted their revenge...
The third evil was the invasion of the Wainriders, which sapped the waning strength of Gondor in wars that lasted for almost a hundred years. The Wainriders were a people, or a confederacy of many peoples, that came from the East; but they were stronger and better armed than any that had appeared before. They journeyed in great wains, and their chieftains fought in chariots. Stirred up, as was afterwards seen, by the emissaries of Sauron, they made a sudden assault upon Gondor, and King Narmacil II was slain in battle with them beyond Anduin in 1856. The people of eastern and southern Rhovanion were enslaved; and the frontiers of Gondor were for that time withdrawn to the Anduin and the Emyn Muil. (At this time it is thought that the Ringwraiths re-entered Mordor.)
Calimehtar, son of Narmacil II, helped by a revolt in Rhovanion, avenged his father with a great victory over the Easterlings upon Dagorlad in 1899, and for a while the peril was averted...
Sunilda - a young woman of the Wainriders (aka Easterlings)
Ervig - her younger brother
Amalfrida - Sunilda and Ervig’s mother (she is also Grimald and Berenga’s daughter)
Grimald - Northman living among the outlaws in the Forest of Mirkwood
Hagan - a young outlaw, Grimald's natural son, freeborn, of an unnamed mother
characters named but not present:
Marhwini - leader of the Éothéod
Calimehtar - king of Gondor
Berenga - Grimald’s wife and Sunilda's grandmother
Maraulf - another of the outlaw leaders
Sarus - a chieftain of the Easterling tribe