159 yards NW of the Cutlass Isle marker facing west behind a pillar
In 1945, six members of the Freedom Phalanx met on Peregrine Island to save the world. The clever Dr. Mnemonic had synthesized an antidote to the poison gas Nemesis had released across the country, but it had to be distributed quickly. With only minutes to spare, these six heroes took off across the country carrying large batches of the airborne antidote. They managed to get the antidote to each infected city, preventing a disaster of epic proportions.
Directions are hard. Put a thumbtack in the centre of the rikti ship on the map (the pale blue dot). It's 560 yards north east of that. It's on a piece of ground sloping steeply up to the West, on the northwest corner of a broken building.
On this site, Statesman and Maiden Justice battled a horde of Nemesis' strange steam-powered robots. The robots' fatal flaw was their inability to adapt to new situations; once events started to transpire differently than Nemesis had envisioned, the robots were next to useless. Maiden Justice used her cunning stealth powers to confound the robots, while Statesman relied on his awesome strength. In the end, they had defeated some six hundred robots, freeing Paragon City from Nemesis' grasp.
The best way to describe is location is to direct someone to enter the sewers in Boomtown and then head East towards the Steel Canyon Sector. The plaque is located on a wall at a junction point connecting the Boomtown, Steel Canyon and Underworld sectors.
In 1945, the Freedom Phalanx was determined to thwart Nemesis' campaign to wrest control of the U.S. Paragon City was one of the many major metropolises Nemesis had infected with his strange poison gas. Using his powers of extra-sensory perception, the Dark Watcher journied into the bowels of the city. Her, in the sewer network, he found storage tanks full of the gas, slowly leaking their noxious fumes into Paragon City's enviroment. The Dark Watcher disposed of the gas, making it possible for the city to be cured.