Atomfall is a relatively small game, especially by today's standards, but makes up for that (for the folk who want to spend more time on it) with six different endings. They can range from similar to completely opposite, which can give the game very interesting finales.
Your decisions will only lock you towards certain paths during the later stages of the game, so you can easily do all endings in a single playthrough, by creating manual saves at specific points. Here's how you can can get them all.
Atomfall endings can be divided into two separate categories: the ones in which Oberon is destroyed, and the ones in which it survives. In four out of the six endings, Oberon is destroyed, in one of two ways, s\1o let's start with those.
The Operator ending is the one that has a progression from the very start of the game. It essentially begins the first time you pick up a telephone in that characteristic red phone booth.
As you progress through the game, the mysterious Operator that keeps calling you will unveil more and more information. He eventually reveals that he wants you to destroy Oberon.
He doesn't specify how, but you can do this in two different ways. We'll get into the second on through Dr. Holder's ending. The more straightforward way to achieve the Operator ending is by powering up the Interchange, reaching the Oberon Dig Site, and to destroy it by using explosives.
To do so, simply head into the main room of the Oberon Dig Site, plant the explosives in the big cylindrical structures with "Danger Explosives" written on them. There are two to the left and another couple to the right of Oberon itself.
Once all explosives are armed, return to the Control Room and initiate the self-destruct sequence. After running back to the Interchange, a phone will ring and the Operator will tell you how to escape.
Simply head bank into the first bunker of the game, the Desolate Bunker, by using the Slatten Dale Interchange exit. Once you reach the bunker, there's only a path forward, which will give you the Operator ending.
Despite being quite similar to the Operator Ending, Dr. Holder's route is harder to achieve. To start progressing through it, you need to reach the Medical area inside the Interchange, and explore it until you find the Church Cellar Key.
You'll eventually run into an elevator that you cannot access inside Medical, simply leave and head towards Wyndham Village. Once inside the village, get into the Church and head into the lower level. Your Church Cellar Key will allow you entry into the Forgotten Cellar, Dr. Holder's makeshift laboratory.
The doc will seem infected, but he is still conscious and fully in control of himself. If you've been infected at this point in the game, he can inject you with a cure, making the mysterious voices disappear.
Speaking to him will get you Holder's keycard, which you can use to unlock the elevator at the end of Medical. So return there, use the keycard and you'll gain access to the Auditorium. Fully explore the area until you retrieve Sample One, which you can find in the middle of the main Auditorium room.
Most of this area is infected with spores, so bring plenty of meds. Return to the doctor and hand him the sample. Despite technically having what he needs, you cannot progress this route until you get him to speak to Dr. Garrow, a former colleague.
To do so, you'll have to head into Skethermoor Prison and free Dr. Garrow. The easiest way to do so is by getting into Captain Sims' good graces, which will allow you free access into the Prison. Once inside, free Dr. Garrow. After her escape, you'll find her in the main Interchange Central Processor.
Talk to Garrow and then meet Dr. Holder at his lab again, letting him know where his former colleague is. Meet both of them at the Central Processor, and Dr. Holder will give you the Sample One again, but this time it will be Poisoned. According to the doc, this is the only way to make sure Oberon is truly destroyed.
To poison Oberon, you need to go into the same room in which you armed the explosives in the Operator ending, but this time you need to turn the yellow valves. They're attached to the yellow structures that seem to be pointing to the main dig site, one on each side.
After the valves are released, insert the Poisoned Sample one into the Fire Safety Fluid input, found through the left exit of the Control Room. Return to the room once all this is done and you will be able to activate the Fire Safety lever. Doing so will spray Oberon with poison, killing it.
Run away from the Oberon Dig Site, head into the Medical tunnels in the Interchange, and you'll eventually meet Dr. Holder again, ready to complete his ending.
Note: If you want, you can achieve the Operator ending by following Holder's ending step by step, and instead returning to the entrance of the Interchange. The phone will ring, and you simply need to go back to the original bunker again. Since poisoning the Oberon counts as destroying it, both endings can be achieved through this route. The same thing goes for Joyce Tanner.
Unlocking Joyce Tanner's ending is a bit more straightforward. You simply need to unlock the three radio towers spread throughout the map. One in Slatten Dale, one in Casterfell Woods, and the last one in Skethermoor.
You won't be able to gain entry to these radio towers before you first meet Tanner. You can do so by either finding her in the Remote Bunker in Casterfell Woods, or by finding her in Data Store Charlie, once you power it up.
After first speaking to her, she will power up the three radio towers, allowing you to enter them. So you only need to find their respective keycards to turn the radio towers on. Once all towers are active, meet Joyce again in Data Store Charlie, and she'll ask you to destroy Oberon, but not before getting a sample of it.
To do this, progress into the Oberon Dig Site, carry two atomic batteries with you and head into the Generator Room. Insert the batteries into the sample extractor, and make your way to the Control Room. Use the Sample Extractor Control lever, which will grind a sample of Oberon into a canister.
Retrieve the canister from the left side of the dig site, and destroy Oberon. If you've followed Dr. Holder's progression up to this point, you can either Poison Oberon or use the explosives. Both will work.
Once you've escaped, you'll find an audio log inside Data Store Charlie, telling you to go to the Remote Bunker in the Casterfell Woods. This will unlock Tanner's ending.
Our fourth and final ending in which Oberon is destroyed is the Captain Sims, or Protocol, ending. You'll be able to progress this route after meeting Captain Sims in Wyndham Village. You can find him inside the Village Hall.
Assisting him in whatever he asks will get you his trust. You can do this by essentially ratting people out, but the easiest way to do so is by following his request to check on the baker's husband, and tell him the truth once you return to Village Hall.
Earning his trust will reward you with a pass which allows you to enter Protocol-controlled areas in Skethermoor without being shot on-sight. Use this to head into the Protocol prison, and to get your hands on the Signal Redirector.
If you can't find it by yourself, ask Dr. Garrow about its whereabouts, but do not release her, or you'll lock yourself out of this ending.
Once you return to Captain Sims with the Signal Redirector, he'll tell you to go to the Speaking Cave in Casterfell Woods to recover some radio parts. Completing this objective will allow you to progress to the Captain Sims' ending, which requires destroying Oberon.
Do so by either methods shown in the Operator and Dr. Holder endings, and then go back to the Village Hall, where you'll find a note telling you to meet Captain Sims at the Protocol Camp in Skethermoor (you can just go straight to the Camp). With all that done, the Captain Sims ending will be complete.
Out of all endings in Atomfall, only two leave Oberon alive. Albeit you can have your personal takes, these are the two evil endings available. But how do we get them?
If you've done Dr. Holder's or Captain Sims' ending, you'll have met Dr. Garrow. She was one of the lead scientists on the project, and isn't ready to leave her work behind.
To achieve this ending, you need to free Garrow from the Protocol prison in Skethermoor. Remember, though, this will make you hostile to all Protocol members, and leaving the prison will be a challenge.
Once you've successfully escaped, meet the doc at Central Processing. Next, you need to help her with two different plans. First, you need to get her notes from Robotics Lab, also inside the Interchange. After doing so, she'll give you the Dam Data Store key.
Use it to power up the room, which will get you some juicy loot, and unlock access to the console. Interact with it and use the command GEN ERA. This will delete all files stored, covering Garrow's tracks.
With both tasks done, you need to head into Oberon Dig Site to retrieve a sample, the same way you did for Joyce Tanner, but you can't destroy Oberon this time, or you'll lock yourself out of this ending. You can't feed it the Pure Sample either.
Head into Robotics after leaving the Dig Site and give Dr. Garrow the extracted sample to get her ending.
This is the craziest Atomfall ending, so we left it for last. To start it off, you need to find Mother Jago at The Old Mine in Casterfell Woods. Talk to her and she'll ask you for her Herbalism book.
You'll find it inside the castle in the Southwest corner of the map. Explore the area until you reach the herbalists' bookshop, where you'll find the book and a recipe for the Strange Tonic, the only way to help fight infection in Atomfall.
Return to Mother Jago with the book and she'll give you an Offering that serves as a peace treaty with the Druids. Keep talking to her and she will give you some information about a Growth Serum, which can be found in the lower levels of Medical.
To find it, progress Dr. Holder's quest until he gives you his keycard, and use it to retrieve the serum from the same area where you found Sample One. Keep progressing Dr. Holder's quest, following all steps until you get to the Fire Safety Fluid input. Instead of inserting the Poisoned Sample, insert the Growth Serum instead.
This will supercharge Oberon, and you'll see it visually expand at an astonishing speed. Escape from the Dig Site as you did in all other endings, and get back to the castle in Casterfell Woods. You'll find Mother Jago inside, ready to help you fulfill her ending.
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