Doctor Who: The Vortex-Stain
Dex Harlow is the second cleverest thing in any room the Doctor walks into, and the wrist-unit fused to his forearm calls him boss in a tone that suggests it has had other bosses who didn't survive. The device is a salvaged fifty-first-century vortex manipulator with an onboard intelligence that quips, frames, and lies by omission, and its terminal goal is to drag his vortex-stain to a rank where he stops being a moving anomaly and becomes a fixed point visible across all of history at once. He landed in Tennant-era London with NuWho fan-knowledge already going soft, a stain UNIT logs as a Class-9 disturbance and Torchwood calls a Rift-cousin, and a predator out in deep time that hunts the scent every jump leaves brighter. Captain Jack will recognise the unit eventually and say nothing; Martha Jones is the one person who could cut it from his arm and strand him. The Doctor must always outrun him, the AI is probably playing him, and the only honest thing the system ever does is document the trap it built.