- "Aemond was the blood of the dragon, and dragons don't cower behind city walls. He marched the king's army north to take back Harrenhal from Rhaenyra's husband Daemon. But when he and Criston Cole reached the castle, they found the gates open, with Daemon and all his men gone. That night they feasted their victory; Daemon had fled rather than face their wrath. But Daemon was more snake than dragon; as Aemond marched north, he'd flown Caraxes south, slithering past the Green army over the waters of the Gods Eye."
- ―Robert Baratheon
The Retaking of Harrenhal was a distraction tended by Daemon Targaryen to remove the forces loyal to the ill-fated King Aegon II of King's Landing, making it easy for him and his wife Rhaenyra Targaryen take the capital mounted on their dragons.
Upon arrival, they found the gates open and the castle empty. Despite the Greens interpreting this as Daemon's cowardice, Daemon had actually flown Caraxes overhead their army, in order to join his wife, Rhaenyra Targaryen, for the conquest of King's Landing.
This absence of the Green Army led to the Fall of King's Landing, in which Aemond's mother, Alicent Hightower, and sister, Helaena Targaryen, were given up by the small council, after which Helaena committed suicide. Daemon and Aemond finally settled their feud during Battle Above the Gods Eye, in which Daemon, Aemond, Caraxes, and Aemond's mount Vhagar, were killed.
In the books
Prince Aemond believed Daemon and his host at Harrenhal to be the real danger. Aemond and Ser Criston Cole rode from King's Landing with a host of four thousand and the dragon Vhagar into the Riverlands. Daemon knew of their plans before Aemond had left the capital, however, and he hastened south on Caraxes, staying well away from Criston's line of march. Aemond and Criston found Harrenhal abandoned after a nineteen day march, believing themselves victorious.