This is shown from the POV of aspen, Percy's twin brother. He and Percy were being dumb at camp half blood and took a cursed pair of friendship necklaces, tying their souls together. Whatever happens to one the other feels/is dragged along to. The necklaces took the shape of twin gold tridents on string chains.
Now, onto the sneak peak!
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"PAUL, MUM!! ME AND PERCY ARE OFF TO CAMP!"
I called through the house, as my twin brother Percy rushed to meet me by the door. My mom sally walked into the kitchen, where the door connected to the house, smiling brightly. "Okay boys, just be careful okay? I know you were promised safety, and as much as i wish to believe them this time we both know the gods have a history of breaking deals." After a few more minutes of saying goodbye (which i promptly forgot) me and Percy managed to get out the door, where annabeth was sitting in the camps minivan, with Leo in the middle row of seats, and me and Percy's half brother Tyson sitting excitedly in the seat to the right of Leo. "Hi Leo, hi Tyson!" I said, climbing into the back of the van with Percy, since annabeth wouldn't trust any of the four in the car to sit in the front seat.