|The following is based on Creation Club content and is not canon.|
The quest starts off by traveling to the church located west of Hyde Park and heading to the upper floor. Apart from the raiders inhabiting Hyde Park, note that enemies may also be randomly encountered at the church. On the second floor, the corpse of Nunez holds Nunez's note, revealing that the Commonwealth Minutemen under Captain Mercer are aiming to retake the Quincy ruins from the Gunners. A legendary laser musket can be found nearby.
After reading the note, head east of Hyde Park and look for the warehouse, located by the water's edge. Inside, a set of Gunner T-51 power armor can be found alongside the corpses of Alexandra Trumbull and a Gunner scout. The Gunner scout's note reveals that they killed each other. Take Trumbull's power armor designs from her corpse, which will unlock the Minutemen Armored Cavalry, Minutemen Patriot, and Minutemen Revolutionary power armor paints. Repaint the power armor suit with one of the three paints and then head towards the Quincy ruins to join the fight. Note that approaching Quincy without wearing the power armor will still start the fight.
The fighting will start once Quincy is entered. A Gunner commander who wears power armor will be singled out and must be killed, supported by the other Gunners around Quincy. Clint, Baker, and Tessa will also be present as enemies if they had not been previously killed. Various Minutemen will spawn to act as friendly backup. After the commander is killed, climb to the top of the Quincy Apartments and pick up the Minutemen flag from Captain Mercer's corpse. Planting the flag on the nearby flagpole will complete the quest. Note that all Gunners within Quincy must be killed before the flag can be planted.