Precipice of War is a Railroad main quest in Fallout 4, and takes place immediately after the quest Underground Undercover.
With The Railroad emboldened by their newest heavy, Maxson and his Brotherhood of Steel have found a new threat in the resistance, and the time has come to eradicate this threat at its core. With their HQ now under direct threat, and exposed to all of their enemies, the Sole Survivor and the Railroad survivors will have to use all of their cunning and limited resources to deal with the power armored threat.
- The Sole Survivor will be notified that the Brotherhood of Steel have already begun an assault on the Railroad HQ, and that their numbers will soon be coming through the escape tunnel. The Sole Survivor will need to join the resistance in order to push back the assault, and once the last of them are dead, they will need to then speak with Desdemona for further instructions. Knowing that the Brotherhood of Steel will be back, and that next time they will stand little chance against their superior technology, Desdemona deduces that the catacombs are the only way out, and that the HQ must be abandoned.
- Traveling through the catacombs, the Sole Survivor will catch up with Glory, who has been critically hurt, in which a short exchange will take place between the two, in which she will then succumb to her wounds.
- Fighting through the catacombs until reaching the main floor of the Old North Church, a Brotherhood of Steel knight will burst through the wall in power armor, in which they will need to be dealt with, as well as the other reinforcements which have taken over the church.
- Once the Brotherhood of Steel have been officially defeated in both the HQ and the church, the Sole Survivor will then need to meet back up with Desdemona and the rest of the survivors, in which they will take some time to grieve over the loss of Glory
- Afterwards, Desdemona will begin planning for the destruction of the Brotherhood of Steel, in which the next step is to destroy the Prydwen. At this point, she will tell Tom that operation "Red Rockets' Glare" is a go, in which both the Sole Survivor and Tom will need to travel to the Cambridge police station in order to secure a vertibird.
- With the vertibird found on the roof of the station, the duo will need to fight their way through the station's Brotherhood of Steel defenses, which are primarily made up of initiates and scribes.
- Once the vertibird has been secured, Tom will explain that the Prydwen remains airborne because of bags filled with hydrogen, and will then hand the Sole Survivor an explosive charge that needs to be used to destroy said bags.
- Once the hydrogen bags have been dispenses, the Sole Survivor will retreat to a safe distance, where they will watch the Prydwen crash into the airport underneath, in which a surviving enemy vertibird will arrive and attack the duo while Tom is preparing the vertibird for lift-off. Once the survivors have been dealt with, find and talk to Deacon to complete the quest, and start the quest Rockets' Red Glare.
- Should Deacon not be an active companion, he will proceed to follow Tom throughout the quest.
- In order to secure Maxson's equipment, the Sole Survivor will need to plant three explosive charges, in which Elder Maxson will spawn, and can then be taken down. After the Prydwen has been taken down, Maxson's gear can no longer be acquired under legitimate means.