"There are no sides. Only people who help you and people who don't."
Background
On the run from The Network for as long as she can remember, Jessica is a recluse. Socially awkward with a directness that is disarming yet capable of manipulation and deception, she is a survivor and a fighter with grey morals who prioritizes self-preservation.
Her musical lietmotif is "Jessica Gets Off" and its Season 2 counterpart, "Fascinating Child."
Jessica's father is the creator of Janus and The Utopia Experiments, Philip Carvel. She was raised from the ages 4-10 by a man named Krystos who taught her how to fight and survive. "Hyde" is not her birth name, but a name given to her by Krystos.
Season 1
Throughout Series 1, the question on everyone's lips is, "Where is Jessica Hyde?" Arby and Lee are searching for her (and the Utopia Part 2 manuscript) and killing everyone who gets in their way. They torture Wilson Wilson for information on her whereabouts before he has even met her and remove his eye in the process.
After Wilson, Becky, and Ian Johnson have congregated at Becky's house, Jessica arrives on their doorstep, telling them to come with her or else they will die. They are hesitant to follow her at first, but she convinces them that she is their best shot at survival.
She proceeds to break into homes, hijack vehicles, and commit armed robbery, acts that shock Ian and especially Becky. Becky and Jessica have a tense relationship from the very beginning; Becky is morally scandalized by the lengths Jessica will go to get the things they need as well as jealous that Jessica's favourite within the group is Ian, in whom Becky is romantically/sexually interested. Jessica takes Ian on reconnoissance missions separate from Becky and Wilson and teaches him how to steal cars, use guns, and conduct interrogations.
Jessica's primary motivation is her search for the Utopia manuscript, which she believes will help her get to know her father and learn about her history before she was taken away by Krystos. After Grant Leetham is brought into the group, Jessica takes a special interest in him, because he was last in possession of the manuscript (having left it hidden in Alice Ward's bedroom.) Jessica is able to bond with Grant over his traumatic personal background, telling him, "some of us don't get to have childhoods." She takes him to a motel and gives him a goth makeover to avoid people recognizing him from the press, and then gets him drunk on vodka shots in order to extract the whereabouts of the manuscript.
He takes her to Alice's house and they retrieve the manuscript from under her bed. Before they can leave, Arby arrives with Alice, Alice's mother, and a woman from the police department. Jessica and Grant hide in the bathroom. Arby shoots the police department woman and Alice's mother and demands that Alice take him to the manuscript. She looks for it but can't find it. Grant, worried about Alice's safety, yells out that he has it. Jessica makes the decision to trade the manuscript for the children's lives, and Alice and Grant escape to safety. Jessica hands it over to Arby, who she is meeting for the first time, though unbeknownst to him she had already removed the pages that include the name of Mr. Rabbit and given them to Grant. Arby lets her go, appearing dazed at having finally met her in person. Before he leaves, he asks her what Philip Carvel was like. Jessica tells him that she doesn't know, and it's why she wanted the manuscript.
Jessica returns to the dilapidated mansion where the other fugitives are hiding out, but doesn't make her presence known. She corners Grant and tells him not to tell anyone that he has the selection of manuscript pages. She sees Ian and Becky having their "crisps and fanta" date through a window. Not long after, she corners Ian and puts a gun to his head, demanding that he calls Milner and leave a message saying that he is with Jessica Hyde. Before she lets him go, she kisses him on the mouth.
At some point after that, Jessica meets up with Arby and stays the night with him at an unknown location. She has a traumatic flashback dream to the night she saw Krystos killed, and Arby asks her if she gets those dreams a lot. She comforts herself by clutching a specific stone. She then accompanies Arby to a roadside cafe. She wants him to take her to the manuscript, but he is reluctant and stalls. He tells her that it's good to meet her in person and describes himself as "a fan," introducing himself as Pietre. Pietre buys her food at the diner that she refuses to eat, calling it "slop" and saying that "only a dog would eat this shit." Following this, he takes her to a field with a tree in the centre. Upon seeing the tree, Jessica becomes distraught; it's the tree Krystos was tied to while he was tortured and then killed. Pietre tells her that he was the one to kill Krystos, when he was only 15 years old, and that despite torturing him Krystos refused to give up any information about where Jessica was hidden. Pietre says, "I wanted you to know that you were loved. Because I wasn't," and urges her not to go looking for the manuscript, but says he will take her to it anyway, just not at the point of a gun. Jessica, emotionally raw, tells him that she doesn't need a gun to kill him.
Pietre takes her to an abandoned industrial building that used to be a Network laboratory and tells her that it's where he grew up. His bedroom is a one-room cell with cement walls and a cot. He shows her a stone that is the same kind as hers, and he tells her that Carvel gave it to him. He says that Carvel said that this rock is so old that it "gives you permission to do anything, because ultimately we're all just the blink of an eye." Jessica realizes the implications of this just before he admits that he is Carvel's son (and her brother) and that Carvel experimented on him as a child. She takes the manuscript even as he warns her not to find out what he did about their father, and leaves him in the burning building.
Jessica returns to the mansion with the manuscript in hand. She is frantic, demanding the pages that Grant hid; however, Grant was picked up by the police, and no one knows where the pages are. Jessica eventually finds them (with the help of Alice), and finds out that the name of Mr. Rabbit is "Letan." She enlists Wilson to use his hacking abilities to search the UK Government servers for mentions of the name Letan. They eventually find it mentioned in a footnote of a Defense Department meeting of the Committee of Genetic Discovery. She plans to find out who each of the men at the meeting were, so she can go and kill each of them to ensure that Mr. Rabbit is removed. Becky tells her to calm down and that she's not acting like herself, causing Jessica to lash out even more. Before she leaves for her killing rampage, Michael Dugdale identifies the Assistant in a group photograph of the men at the meeting, and so Jessica (with Wilson in tow) proceeds to the Corvadt building in order to kill him.
After they break in, Wilson turns on her, making his pro-Network allegiance clear. He pulls a gun on her but is distracted by the sudden arrival of Grant, and Jessica is able to knock him down. She reunites with Grant, who indicates that he has killed the Assistant, and she gives him a hug.
The two of them leave Wilson in the Corvadt building and return to the mansion, where Dugdale, Ian, and Becky have returned from burning down the warehouse containing the Russian flu vaccine. Believing that the dust is finally settling, Ian tells Jessica that in order for the Network to be truly finished, she must take the manuscript to Milner. She reluctantly acquiesces and brings the manuscript to Milner's office at MI5 headquarters. When Milner steps out for a few moments, Jessica notices that on her desk is the same stone that Carvel gave to both Jessica and Pietre. This is the final piece of the puzzle needed for Jessica to realize that Milner, rather than the Assistant, is the true Mr. Rabbit.
Jessica attempts to escape the building but is cornered on the roof. She burns the manuscript, an act that brings her to tears, but Milner reveals that they were never really after the manuscript, but instead Jessica herself. Milner shoots her in the leg before she can escape over the side of the building, and tells her, "[Carvel] called you his greatest achievement, and that's where he hid Janus." The Janus serum was injected into Jessica's bloodstream before Carvel was separated from her, making her its living host.
Season 2
Jessica is held captive by the Network in a cell inside a large glass pyramid structure in the middle of nowhere. They have been attempting (via torture and persuasion) to extract information from her on the nature of Carvel's last-minute adjustment to Janus, but she hasn't talked. She is under extreme high security, having brutally killed all of her previous interrogators. She is introduced to a new interrogator named Ross, who takes a gentler approach, engaging her in dialogues about her feelings towards her father and the fact that she can never have children, being presumably sterile. Over time, Jessica appears to thaw towards him. She also begins reading the Bible.
Eventually Jessica reveals her true plan: to get Ross to trust her enough that she can lure him into a death trap she has rigged up from the automatic mechanism built into her cage and a noose she crafted out of Bible pages. Though Jessica ends up being put back into her cage under even higher security, she keeps the spring she stole from the inside of Ross' pen, and keeps it on her body.