Warning: spoilers for the Fallout TV show follow.
If you’ve watched the Fallout TV show, you might have been left wondering exactly what Thaddeus ingested that resulted in his mysterious healing powers.
While the Snake Oil Salesman who gives Thaddeus the concoction suggests the Brotherhood of Steel squire need not worry about radiation having ingested it, and Lucy MacLean and Maximus later wonder whether he’s turned into a Ghoul after demonstrating remarkable healing powers, fans have a theory that helps explain exactly what Thaddeus has taken.
Fallout lore expert TKs-Mantis, who IGN has covered before in relation to the TV show’s Brotherhood of Steel airship, which suggests one of two Fallout 4 endings are canon, believes this serum to be the ‘Mysterious Serum’ from Fallout 4.
I am nearly positive that Thaddeus was given a vial of Mysterious Serum from Fallout 4. It tracks.
— TKs-Mantis (@TKsMantis) April 17, 2024
"This serum is derived from the blood of archaeologist Lorenzo Cabot, who discovered a mysterious artifact during an excavation in the Rub' al Khali in 1894. The artifact granted… https://t.co/ckQqstyPvq pic.twitter.com/7C30kovY7f
In Fallout 4, the Mysterium Serum originates from the blood of a late 19th century archaeologist called Lorenzo Cabot. Cabot gains immortality and superhuman abilities after finding an artifact during an excavation. There’s a whole sidequest about the Cabots, who use this serum to live for centuries.
The item’s description mentions a powerful anti-radiation effect, which would explain the Snake Oil Salesman’s comments to Thaddeus before he makes his quick exit. The healing would reasonably fall under superhuman abilities, too. In Fallout 4, the Mysterious Serum grants +5 Strength and +50 Damage Resistance, as well as -36000 Radiation.
The Mysterious Serum isn’t the only theory fans have come up with for Thaddeus’ potion. Some believe it to be the ‘Healing factor serum’ from Fallout 76. In the game, the Healing factor serum grants the Healing Factor mutation and suppresses its negative effects for an hour. This would track with the remarkable healing we see Thaddeus demonstrate in the TV show.
Twitter user Aaron Rigby has another theory, which taps into major spoilers for the end of season one: “ would love to see this be the mysterious serum... But it is far more likely that it is the byproduct of Barb Howard's side of Vault-Tec. She likely used the compound on Cooper, ya' know to ‘save him’ in her way. Now it's in the wild.”
And here’s another theory: that Thaddeus has taken a form of the Forced Evolutionary Virus, or FEV, and is now on his way to becoming a Super Mutant.
Of course, fans may be overthinking this whole thing, and the Snake Oil Salesman’s serum may in fact do exactly what the characters suggest it does: induce ghoulification. With a second season looking likely, hopefully we’ll find out.
Speaking of Fallout lore, IGN recently interviewed Bethesda's Todd Howard, who also serves as an executive producer on the Prime Video series, as well as Jonathan Nolan (The Dark Knight, Interstellar, Westworld), executive producer and director of the first three episodes of Season 1, to talk all things Fallout.
Wesley is the UK News Editor for IGN. Find him on Twitter at @wyp100. You can reach Wesley at wesley_yinpoole@ign.com or confidentially at wyp100@proton.me.
