“Principia” is episode thirteen of season five of Marvel’s Agents of S.H.I.E.L.D.
In the previous episode, “The Real Deal”, Fitz and Simmons got married, and Deke had found a wedding ring for Simmons that looked just like the one his grandmother had. General Hale’s people were also trying to work out who Deke was – and found he is genetically related to Fitz and Simmons. Which suggests that the ring Deke found isn’t just one that looks like his grandmother’s – but is that ring.
The episode opens with a psychiatrist of some type talking to a young man he calls Alex. He is telling Alex that there is talk of giving him a high dose of the drug thorazine to stop his violent outbursts. The doctor wants Alex to talk about his experiences, the beatings his father gave him and his experiences with S.H.I.E.L.D.
Alex says that he remembers everything, then starts telling the doctor about the latter’s daughter, who has just turned three, and repeats things he overheard the doctor discussing with his wife on the phone during a previous session. It seems Alex does remember everything, including the doctor’s address, and stabs the latter in his hand with a pen. For Alex is perhaps better known as Werner von Strucker, last seen in “Bouncing Back”.
Yo-Yo is still recuperating in bed with Mack fussing over her to the point of annoyance, with Simmons taking care of her. Coulson enters and tells Yo-Yo that Fitz is going to make her prosthetic arms, they just need some materials, and tries to sell her on their benefits. But he admits they aren’t the same as the real thing. Yo-Yo wants to know what Mack will think if she has robot parts, and he says that they aren’t the parts that matter. Which he totally does not mean the way it sounds.
The rift to what Fitz calls the ‘Fear Dimension’ was sealed in the previous episode using the gravitonium in Deke’s belt buckle, but it seems that this is only a temporary fix and they need more gravitonium for a permanent solution. Which is a bit of a problem as it’s not that common on Earth.
Cybertech was the last place where any significant amount of gravitonium was seen, but all the scientists who worked at the company are dead. However, according to Daisy, their death certificates were all signed by the same man. Which looks a bit too coincidental, so the team is going to have to head outside to find him. Coulson asks Deke, who has had more experience with gravitonium than any of them, to help Fitz. Which Fitz does not appreciate, as he finds Deke a bit annoying (until he proves helpful, anyway, and then perhaps still somewhat annoying).
Coulson and the others find the man who signed the death certificates, and he is not at all willing to cooperate. Until, that is, Mack recognises him as Tony ‘Candyman’ Caine, a roommate from his first year at the S.H.I.E.L.D. academy – until he was kicked out, anyway. At this point, Caine becomes more willing to help. He explains that, just like Operation Paperclip at the end of World War II where Nazi scientists were recruited, former HYDRA scientists had the same thing done. Caine helped fake their deaths and set them up with new identities.
Caine leads them to the scientist, who says that all the gravitonium was placed on a ship, the titular Principia, but the ship sank in a thunderstorm and is now under 5 miles of water. Which would make retrieving the gravitonium a bit tricky (this is where Deke proves helpful).
Von Strucker has been taken from where he was being treated to the same place that Ruby is being kept. General Hale – who seems to have had some seriously dubious connections in her past – had said she was assembling a team, and at the end of “All the Comforts of Home” had found Carl Creel.
Yo-Yo is thinking that the future they saw is inevitable. Daisy seems to think that they could also use Cybertek technology to save Coulson’s life, but he isn’t interested in artificially extending his life again. Daisy and May are not going to listen to him.