The Final Crisis Point
These are the events of the Silver Agent's first (or last depending on your view) time traveling jumps, to a crisis point in Astro City's history. This one was in July of 1984.
Prior Crisis Points
Previously the Agent had returned from the far future in 1982, to help stop the destruction unleashed with the Rise of Kerresh the Devastator. Before that he arrived during the 1977 Gang War, and stopped Black Velvet's darkness power from turning the whole city mad. And his last(or first) was in 1973 during Madame Majestrix's Invasion to broker peace talks which led to her standing down and not ripping North America apart.
The Crisis Point
This time the Agent arrived in Las Vegas in July 1984 for the first of the major crisis points from coming from the future. He found local hero and former Honor Guard teammate, Mirage, fighting an army of Dynamoids along with Hellhound. Mirage revealed that he found out they were missing hobos being transformed by a front company at a casino. And that the work was being done by Dr. Norton Ganss, who was making troops for the Iron Colonel.
The trio of heroes were trying to make their way to Ganss's machine in order to shut down the Dynamoids. But at the same time Dr. Ganss was in his very lair with his benefactor Aubrey Jason, turning him into one his super powered creation, tapping into the dark energy that was running in the world in 1984.
A pair of vigilante brothers, Charles and Royal Williams were on Jason's trail for a long ago crime against their family. They caught up to Jason and Ganss right in the middle of his transformation and knocked out his machines. This broke the mind of the Dynamoids calling them back to the base and in turn destroyed much of Las Vegas and enabled Jason to get away from them and the heroes.
The Agent contacted Honor Guard to meet him later and the three started helping with rescue of trapped civilians.
At the same time in Astro City, another nigh-powerful figure had crept from nowhere into the spotlight; the Pale Horseman. Whatever vigilantes, like the Blue Knight, had put fear into the minds of Astro citizens, the Horseman topped them all. Riding a flaming stead and acting as his Biblical namesake, he started incinerating criminals at will. And no matter what the crime from murder to petty child thievery, no one was safe from him. In his wake he even killed the reformed Street Angel.
The Honor Guard had tracked down the Iron Colonel, though apparently didn't get much information. While Aubrey Jason, broke into an E.A.G.L.E. facility in Tuscon, Arizona and stole a piece of the Sekhmet Stone, which bolstered his power after he was injured in Las Vegas. A few days later, he returned to Astro City to a former Pyramid base and was feeding off the dark energy and hatred swelling around the city and now calling himself Lord Sovereign.
But Silver Agent and the Honor Guard were back too. With the swirling power all around they could only send one person in with the Puls-Canon and the Agent volunteered himself. After getting himself into Sovereign's base, he found the Williams brothers who had tracked him again as well and enlisted their aide in stopping him. Here he revealed that the rift in reality caused by the Point Man firing the Innocent Gun during the Rise of Kerresh the Devastator, was what let the Pale Horseman into our reality and was the energy source that let Dr. Ganss power Lord Sovereign. And the dark energy was started to seep out into the public. They were feeding on the blood lust and it was evidenced in the heroes and vigilantes popping up at this time. They even cheered on the Pale Horseman's killing of the Street Angel. This was the major crisis that the Agent was trying to fix.
By this time the Pale Horseman had noticed someone trying to tap into his power and came into contact with Lord Sovereign. The battle between the two of them, enabled the Agent to get to the machine powering Lord Sovereign and let the rift collapse upon itself. The two beings then blinked out existence, at least in this reality.
The Silver Agent gave a brief speech, letting the people know that the worst was now behind them, but it was up to them to get through the rest. And this was beginning of the end of the "Dark Age" for Astro City. Things started getting better outlooks and the mood started to change. The people seemed to shake off the darkness and heroes of the like and the heroes started to resemble that outlook.
And on January 28, 1986 when Samaritan's dramatic debut to the world happened, the "Dark Age" was no more and a new age beginning.