The Lighting of the Silver Beacon marked a substantial change in the history of Barovia, as recorded in Curse Of Strahd. For hundreds of years, the valley had been under the complete sovereignty of Count Strahd von Zarovich, who controlled its lands and misty borders through the Ladies Three and Vampyr. Its skies were undercast by a permanent, dismal darkness, and even the light of the moon was obscured by heavy clouds. Horrors awaited in the mists, which would thicken without discernable pattern.
However, a dormant power waited on a mountain in the valley; an ancient Silver Dragon named Argynvost had long ago been defeated by Strahd. Before his passing, he had built a fort to stand against the von Zarovich family's darkness. His Order of the Silver Dragon had used the mansion, dubbed Argynvostholt, to strike back against Strahd's attempted conquest of the valley. These paladins were ultimately defeated after he became a Vampire; Strahd tore Argynvost's skull from his body and kept it as a trophy in Castle Ravenloft. The former knights of the Order could not pass on, becoming Revenants, and a weak Ghost of the dragon himself still stalked the mansion's halls.
At the behest of Sir Godfrey Gwilym, a revenant who had kept some of his memory, a group of adventurers investigated Argynvostholt. They found the place connected strongly to the Ethereal Border and its halls occupied by Undead paladins, unable to move on due to their vow they had sworn to their Captain, Vladimir Horngaard. All of the revenants had lost their mind, but Vladimir in particular had become completely overwhelmed by his hatred for Strahd. Believing Barovia to a be prison of Strahd's own making, he would not allow the heroes to oppose the vampire; he was content to have his retinue suffer in eternity if it meant Strahd could not escape his eternal torment.
Vladimir attempted to kill the adventurers, who barely escaped with their lives, but not before they were able to converse with Argynvost's ghost and learned how to help the Captain pass on. Mormeros Fayan, Tobias Villie Broadnose Cogsmith, and Ajuni Elajoral had come from the Prime Material searching for clues about the Silver Dragon, and wished to lay him to rest. Joined by Ghalwin of the Grove and Ezmerelda D'Avenir, they visited Castle Ravenloft to meet with Strahd; these adventurers would later be called the Heralds of Dawn.
After surviving a dinner with the Count and his spouses, then investigating the castle, they were able to overcome myriad traps and foes to find Argynvost's skull. Relying on magic to temporarily shrink his head, they used the Portal in the catacomb's brazier room and were transferred back to the mountain. Found by Sir Gwilym while in the Svalich Woods, Tobias and Ghalwin both swore vows to the Order of the Silver Dragon, ensuring that its tenets would live on. They all then carried the ancient skull back to the mansion, unaccosted by the undead knights, and reconnected it with his body in the mausoleum.
The head reattached to its body in a shower of cold embers, and suddenly, the mansion's tower produced a spark of hope visible for forty miles. Argynvostholt became a beacon of silvery light, and the revenants of the Order finally passed on.