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Winter of Atom is a sourcebook for Fallout: The Roleplaying Game created by Modiphius using licensed intellectual property from Bethesda Softworks and the Fallout franchise. It is set in and around the Boston Commonwealth and centers on a new sect of the Church of the Children of Atom and their clashes with the existing sects and inevitable war in the Commonwealth caused by their ideological clashes.


Focusing on the brutal winter of 2286, and set just before the events of Fallout 4, the sourcebook is divided into three narrative chapters, each of which introduces an overarching story arc, and is all tied together into a massive story detailing the survival of the Commonwealth against a new sect of the Church of the Children of Atom led by the Last Son of Atom.

Welcome to the Commonwealth[]

The first chapter is titled Welcome to the Commonwealth, and starts with The Train Job, where the player characters (PCs) lead a multitude of refugees to the outer gates of Diamond City, only to discover that the settlement is overcrowded and facing a scarcity of food supplies. In order to gain entry, the PCs need to locate a plundered supply train outside the ruins of Boston to retrieve essential provisions. Pursuing the culprits, the PCs encounter a recently arrived member of the Church of the Children of Atom, who is in search of a revered prophet known as the Last Son of Atom. As the characters venture further into the Commonwealth, interacting more closely with its inhabitants and completing auxiliary missions, the severity of the impending winter becomes increasingly harsh.

Cleansing Fire is a highly lucrative assignment—to assist in establishing a secure trade route through an underground sewer system to facilitate the delivery of food to needy settlements. As the PCs explore the depths of the sewer, they come across two distinct sects of the Church of the Children of Atom and must make decisions on how to handle them in order to ensure a safe passage for neighboring communities. Meanwhile, as the influence of the Last Son of Atom's disciples grows, the coldest months of winter set in.

In the midst of A New Eden, the PCs find themselves sharing a campfire with a courageous group of Minutemen, who may have discovered a new source of sustenance from a stranded cargo ship called the USS Germination. However, it soon becomes evident that Dr. Yarrow, the leader of the vessel settlement, has poisoned the Minutemen and others who consumed his eerie flesh-like fruit. Consumption of this peculiar fruit induces debilitating starvation and gradual transformation into monstrous beings. Racing against time, the PCs find a cure for the affliction and potentially render the massive food supply of the USS Germination safe for consumption by the settlements - all the while battling against the mutated sailors aboard the ship, as well as soldiers of the Last Son of Atom, who seek to claim the vessel and convert it into a fortified stronghold for their expanding army.

The Winter War[]

After their harrowing experience aboard the USS Germination, the group arrives at a besieged settlement under attack by the Gigapede, a colossal mutated centipede seemingly impervious to harm, accompanied by a small contingent of soldiers loyal to the Last Son of Atom. In A Thousand Feet of Terror, the players bravely defend the settlement and successfully capture an Atomite soldier for interrogation. Extracting information from the captive, they uncover the target of the Atomites' next assault, allowing them time to travel and prepare for the impending battle.

In the subsequent clash against the Gigapede, the group confronts a highly trained unit of fanatical cultists determined to obliterate the settlement in the name of their atomic deity. During the encounter, the group learns that the Gigapede's handlers issue commands to the siege creature using American Sign Language. In the aftermath, they face a critical decision with only a few days at their disposal: how to best equip themselves for the impending invasion by the Atomites. They can rally support from allied settlements, scavenge for formidable weapons and armor, or even acquire enough proficiency in ASL to communicate with the Gigapede directly.

The chapter reaches its climax with a third and final confrontation against the Gigapede. United with their allies, the group makes a last stand against the Last Son of Atom's relentless army, becoming the sole barrier standing between the Atomites, the Gigapede, and the safety of their cherished home. Once victorious, with the promise of a brighter spring on the horizon, the Commonwealth embraces a hopeful peace and embarks on reconstruction.

The Day of Division[]

The enigmatic Last Son of Atom persists in his pursuit beneath the Whately Research Facility, located in the Glowing Sea. He unearths an ancient, long-buried city that potentially predates recorded human history. Within its depths, he discovers a peculiar artifact that has haunted his dreams for years—an extraordinary crystalline device dubbed Atom's Glow. Driven by his desire to exploit its reality-altering power, he conducts mind-altering experiments, intent on bringing about the prophesied Day of Division. As he delves deeper into his plans to indoctrinate the Commonwealth, his experiments drive his remaining followers and creatures of the Glowing Sea to madness.

Meanwhile, the players encounter a devoted Atom worshipper who wants to deliver a crucial message to them. Embarking Into the Glowing Sea, they receive the missive sent by Mother Isolde, leader of a faction that opposes the Last Son. Isolde claims knowledge of the cult leader's covert base and offers her assistance at the Crater of Atom. The players brave the Glowing Sea, but they must survive a perilous encounter with Sister Dawn — Isolde's daughter, transformed into a towering Glowing One due to the Last Son's experiments.

Upon arrival, the group gains further insights into the Church and the Last Son of Atom. Its denizens are peace-seeking individuals who yearn for redemption within the Commonwealth, but cannot confront the violent cult leader themselves. With intel acquired, the players venture across the hazardous Glowing Sea in pursuit of the Whately Research Facility.

In The Buried City, the group navigates the remnants of a pre-War chemical weapon research facility, fighting creatures and fanatics driven mad by Atom's Glow. As they delve deeper into the facility, inexplicable supernatural phenomena materialize. The PCs uncover the facility's founder, General Whately, ancestor of the Last Son, who was also a cult leader venerating a cosmic deity believed to slumber within the subterranean ancient city.

The players finally descend into the excavation site and the buried city. However, Atom's Glow ensnares their minds, producing utopias and nightmares in their minds. Those who manage to break free confront the Last Son of Atom and any companions ensnared by his influence. When the cult leader reveals his true intentions and extends an offer, the group must decide whether to embrace his vision, fight him, or flee.

What follows are the Epilogues, providing further exploration of potential outcomes and their ramifications for the Commonwealth, while the Future Quests section presents plot hooks and guidance for developing new, high-level quests to follow the nuclear winter.

Factions and locations[]

The book also pertains to several new Commonwealth factions, including Mirage, Big Top, Beatsville and Mechminster Abbey.

Development history[]

Based on his work on With a Bang, or a Whimper and Once Upon a Time in the Wasteland, two adventures provided together with the core rulebook for Fallout: The Roleplaying Game, Donathin Frye was commissioned by Modiphus to lead the new sourcebook project and create a full team focused on it, including Gabe Hicks, Jacky Leung, Chelsea 'Dot' Steverson, Chris Bissette, and Jesse Heinig, one of the original creators of Fallout.

The sourcebook was designed from the ground-up like a proper Fallout game, including a main quest framing the campaign, with numerous side quests and exploration options, taking player characters from level 1 to 21. The sourcebook also introduces new mechanics and encounters tied to the winter season, as well as tools for designing and balancing encounters, expanded rules for traveling and gaining reputation, level scaling, and minions.

Additional origins[]



Major Settlements[]


  • Horace Mann School for the Deaf and Hard of Hearing
  • The Derailed Train, near a tilted radio tower
    • Inside the train car
    • The bandits' bunker
  • Sewer
    • The Platform
    • The Rad Church
      • Small Vault
  • Skyscraper
  • The Glowing Sea




Children of Atom[]

  • Brother Bennett
  • Brother Landon
  • Brother Lockjaw
  • Brother Lucius, a messenger from Isolde's village
  • Brother Lywin
  • Brother Schumaker, a priest
  • Brother Scrapjaw
  • Eliza and Esther, the Children of Atom Tinkerers
  • Lil Boomy
  • Minnie "Muse" Mabee
  • Old Boomy
  • Sister Dawn
  • Sister Gertrude
  • Sister Iris
  • Sister Sunset
  • Thrash, a super mutant woman who leads a gang
  • The Last Son of Atom

Sisters of the Forge[]

  • Sister Amos Nition
  • Sister Guyger
  • The Reverend Riveter
  • Tripper


  • Blackjack
  • Brawny Bill
  • Charlotte
  • Deputy D3N-Z3L
  • Dead Drop Dave
  • DJ Daddy-O
  • Evie
  • Fusion Susan
  • Janie
  • Kate
  • Linda
  • Mackenzie "Mac" Frey
  • Madame Atom
  • Maxwell Kantor
  • Minuteman Reese
  • Norm
  • Ole' Man Murray
  • Regina
  • Ringleader Johnnie Lonnie
  • The Inked Lady
  • The Jambakers, a beatnik jam band
  • The Lama, a guide
  • The Swinging Sals
  • The Twins, Eric and Elana
  • Regina
  • Dr. Yarrow
  • Lieutenant Jake Ripley
  • General John Whately


The following characters from Fallout 3 and Fallout 4 are mentioned by name or appear in Winter of Atom.

Generic NPCs[]

  • Children of Atom
  • Children Of Atom Berserker
  • Children of Atom Fanatic
  • Children of Atom Handler
  • Children of Atom Soldier
  • Children of Atom Shock Trooper
  • Children of Atom Tinkerer
  • Diamond City Security
  • Minuteman Rifleman
  • Mirage Security Guard
  • Neighborhood Watch
  • Robber
  • Super Mutant
  • Pilgrim
  • Scavenger
  • Super Mutant
  • Wastelander



  • Children Of Atom Sentry Bot
  • Children Of Atom Protectron
  • Eliza's Dragon
  • Machine Gun Turret MK I
  • Mister Gutsy Patriot
  • Praying maintenance robots



  • AT-0M power armor
  • Behavioral analysis mod
  • Cryojet
  • Flash bang grenade
  • Grappling gun
  • Magnum-nomicon
  • Memorial battle armor plating
  • Staff of Atom
  • Tear gas launcher
  • Gamma gun
  • Mini-nuke
  • Syringer
    • Lockjoint ammo
    • Endangerol ammo
    • Yellow Belly ammo
  • Geiger counter
  • Pip-Boy
  • Pristine white robes with a green sun embroidered on the breast
  • Welder’s Visor
  • Hancock's hat


  • Chem suppressant syringe
  • Flesh fruit
  • Pew stew
  • Melon
  • Melon juice
  • Corn
  • Tarberry juice
  • Brahmin milk
  • Stealth Boy
  • Magazines


  • Holotapes
    • a man whispers, “I made a mistake. I should never have gone down there. That thing isn’t God.”
    • a woman praying feverishly to the Black Star Who Dreams Beneath, begging to be devoured
    • The Last Son of Atom exclaims, “I found Him! Atom is here. If you are listening, rejoice! The Great Division begins today.”
  • Notes
    • Chemical Weapon Test Patient Coroner Report (scribbled on the back: “Ha ha HA what a GAS”)
  • Church of Atom Propaganda Pamphlet
    • titled “When the River Glows Green”
    • titled: “Divide Us, O Great One!”
    • concerning: "protecting the vulnerable and speaking truth to power"
  • Defaced Church of Atom Propaganda Pamphlet (titled “Catch A Shining Star and Put It In Your Pocket”)
  • Diary of a Muse
  • Sister Dawn’s journal
  • Photo of Dawn
  • Rare Part for Sister Guyger
  • A pendant depicting a long triangle with a thick circle inside it, bisected by a vertical bar, which emits a soft yellow glow
  • Obsidian Statuette of a Tentacled Star (smeared with blood and brains)
  • Whateley's hand

Behind the scenes[]

Winter of Atom received in-depth coverage in an April 2023 Polygon article prior to its release.[Non-game 2]