After defeating the alliance of Airachnid and MECH, all of team Prime, Jack include, thought they would have some time before hearing of Silas and his terrorist organization again. They were wrong. Only a few day later a MECH commando entered his school and kidnapped him.
For months team Prime searched for him without success.
In the mean time Silas somehow captured Airachnid, deciding to use her in an off-shot of his experiment labeled 'project Chimera', along with the young Darby, once her biology had been thoroughly studied. What followed were months of torture for both the mad Cybertronian and Jack, unaware the other was also a prisoner. The spider-con wondered where and how humans could have found a way to restrain her so securely, while Jack searched a way to escape his cell, but without success.
Then came the worst day of Jake's live. The day he woke up secured to an operating table, his head shaved, wondering why he was also secured around his torso, neck and forehead, until MECH's butchers surgically removed his arms and legs, without anesthesia, and immediately connecting the cut nerves with thick cables, before opening his skull to connect his brain to more of those thick cabling. Then, MECH slowly disconnected Airachnid's spark-chamber, replacing it by a connection to Jack instead, before removing said spark-chamber from her chest and placing the teenager there instead.
Jack fell into a restless sleep from the barbaric operation, while MECH operative closed Arachnid torso.
What Silas and his goon never expected was that Jack would somehow gain access to Airachnid memories and knowledge which, among other things, caused him to revive part of Airachnid live from the mad Decepticon's point of view in his sleep, notably the time she tortured both Arcee and Tailgaite, before bringing the second in the same room as the first just to make her assist at the murder of her partner.
He awoke with a start, and tried to look around him, but received conflicting informations. While his human eyes weren't seeing anything since they were in a pitch-black place, he was also seeing through Airachnid compound optics. It took him a bit of time to understand what he was seeing, even though the image was first processed by the 'Con's CPU, but once his brain had adapted he realized what he was seeing: a Cybertronian arm, and not one he was happy to see. It took him a bit longer to realize he was seeing it like it was his own, his panic at seeng Airachnid arm not helping. That said, as soon as he did, he cried "Silas! What did you do to me! How did you put—AGRL!"
Silas and MECH had abandoned the facility as soon as they knew their experiment had worked, leaking its location to the Autobots hopping that Arcee's hatred for Airachnid would make her kill their experiment first and ask question, but they still monitored what was happening remotely. The terrorist leader was all to happy to prevent Jack from saying more by pressing a button, making electricity course through both bodies now occupied by the teen.
Nobody at MECH expected this to trigger the opening mechanism of Airachnid's chest-plate, but it's exactly what happened. Hearing a gasp, Jack looked were it come from with both heads and saw Arcee with a servo over her mouth. "A—Arcee?!" As soon as he said her name, he started to remember all of their moments together, good or bad. It made him happy, but was soon spoiled by Airachnid's memories of her encounters with the two-wheeler also coming to him like they were his own.
Arcee approached her partner, horrified by what MECH had done to him. "Oh Jack… What have they done to you…" She tried to caress the side of his face, but he pushed his head as far away from her servo as he could, a move copied by Airachnid head. "Jack?"
By the time he answered, the other Autobots had joined the femme and their missing friend. "I'm not sure I'm 'just' Jack anymore, Arcee. All of Airachnid's memories, they're still up there, in her head, and I have full access to it, in a way that make them feel like they're mine. Do you understand Arcee?! I remember Tailgate's death like I was the one who caused it, like I was the one feeling joy in extinguishing his spark!"
"I… Can't imagine how traumatic that is. But I know you Jack, even with all of Airachnid knowledge in torture you would never feel any joy in using it, not even with memories saying otherwise. Would you?"
"N-no, no i wouldn't. Thank's Arcee."
Notes: Well, that was dark. Don't worry, not all stories from that collection will be like that.