March 22, 778: Three Northumbrian high-reeves killed, possibly on the king's orders
In the south of England in the second half of the eighth century, the political landscape is quite straightforward. Offa is king of Mercia (757-96), and effectively of most of the other southern kingdoms as well. (Only Wessex seems not to come under Offa's direct control, but given that the the king of Wessex is married to one of Offa's daughters he won't have been entirely independent, either.) Offa corresponds with the Frankish king (later emperor) Charlemagne as with a brother, and (at least for the Mercians) all seems to be going for the best in the best of worlds.
North of the Humber, the landscape looks completely different, with rival claimants, new rulers every few years, simmering feuds, open battles and secret murders -- more like something out of Macbeth. The Anglo-Saxon Chronicle records that on 22 March 778, Æthelbald and Heardberht killed three high-reeves, Ealdwulf Bosa's son, Cynewulf, and Ecga, and that after that Ælfwold succeeded to the kingdom and drove Æthelred from the country.
We know no more about the three high-reeves or the two murderers. We do know that Æthelred had been king from 774-778/9, and that his father, Æthelwold Moll, had been king from 759 to 765 (when he was driven out). We also know that Æthelwold came to power right after the previous king Oswulf was slain by the men of his household (and it seems a fair suspicion that Æthelwold might have been one of the prime movers of the plot), and that the Ælfwold who drove out Æthelwold's son was himself the son of Æthelwold's victim Oswulf. Ælfwold rules for about nine years (778/9-788) before he is murdered, and two years after that Æthelred returns to take throne a second time (790-6).
Review the history, 757-806.