Spoiler warning! This article contains plot details about events that occur later in the game.
Nuclear Plant Epsilon is one of three nuclear plants in the Tandor Region. It is only accessible by a boat from Route 7 on a single visit before the Bealbeach City gym.
Originally abandoned in the same nuclear catastrophe 10 years ago that claimed the life of the player's mother, Lucille, today the quiet and ghostly island is buzzing with activity. Led by Theo's dad, Cameron, crewmen and scientists bustle around the site building a new and safer plant. The construction has not gone as quickly as planned. While the local flora seems to have recovered completely, the irradiated fauna has not.
The crew has been hearing strange noises coming from the old plant entrance on the south of the island, and encountered eerie, glowing, and extremely violent Pokémon. Once captured, these strange Pokémon refuse to obey orders, even turning on and attacking their new trainers. To deal with the situation, the crew shipped in Pokémon healing equipment, creating a makeshift Pokémon Center, and one of the workers has begun selling various supplies inside the rest house. The scientists have started training their own Pokémon to protect themselves, as well as growing Hafli berries to protect their Pokémon from Nuclear-type attacks.
This is the first location the player encounters Nuclear-type Pokémon.
This sidequest focuses more on the game's backstory than providing you with a particular puzzle or challenge. After speaking to Cameron, you are free to roam the island, challenging the scientists and battling wild Nuclear-type Pokémon. The island is experiencing a constant, steady rainfall, meaning all battles outside will take place in the rain. You cannot return to the main game until investigating the nuclear plant itself.
When you've finished battling, capturing Nuclear Pokémon, and leveling up your team, head to the abandoned power plant, located south of the crew's main camp. The interior of the old plant is dark and eerie. Scattered about are various pages from the Burnt Notebook, which once contained notes on research being done at the plant but have since been charred into near-illegibility:
Report #01: Prog -- is ---- --- -- --dename 092. --- ----- --- from radiation-----s biofiber. It ---- -- ---- to reconstru-- --- -- damage-
Report #02: --- power core ------ from over----. It ---- ------ a large ---- -- nuclear fuel to -------. ---- ---- activated- -- --- -- prod--- ---- limitless energy.
Report #04: ---- -- the Interface --- final---- today. Th- -erator - -- ---- - ----- full control -- --e Sp-cimen. ---- chief reseacher, Dr. ----- --s ---- granted clearance.
Report #05: ---- has been - breach -- confidential--. ----- --- ------ shall -- relocate --- undergr-- --. Project 092 --- have -- -- --rminated.
In the back of the power plant near Report #04 is a Rusty Key, which unlocks a door on the far western end of the second hallway. Be aware that entering this door will prevent you from leaving until you finish the sidequest. The door leads to a chamber with a large machine and a single, working computer screen nearby. The screen displays a message about a stasis tank and asks if you wish to start the restoration process.
Regardless of your answer, the floor suddenly gives way, dropping you into a room containing a Lv. 30 Nuclear Trawpint. Little more than a mindless killing machine, it lumbers forward and attacks. While it is Level 30 and quite powerful, it has no Nuclear-type moves, making it less dangerous than it seems. A decent Steel- or Poison-type should be able to resist its moves fairly well, and a powerful Psychic-type can take it down with ease.
After capturing or defeating the Trawpint, the intense radiation in the area makes you pass out. Cameron, realizing you're not answering your radio, sends a rescue team to you. You are brought back to the rest house, treated for radiation sickness, and sent back to Route 7. You are unable to return to Nuclear Plant Epsilon afterwards.