4 ideas
Kazumi Kimura runs Meteor News, a small Tokyo website that turns public orbital data into shooting-star and space-debris forecasts. He notices that a spent upper stage from an Iranian launch is gaining altitude instead of slowly decaying, which a dead object should not be able to do. That single anomaly in a hobbyist's data feed draws him into a covert operation involving hackers, US and Japanese intelligence, and commercial space interests.
A long conductive cable moving through Earth's magnetic field has a current induced in it, and the resulting Lorentz force can raise or lower an orbit without burning fuel. An object fitted with one can look like inert junk yet still change its trajectory with no plume or thrust signature. Observers who assume only rockets move things in orbit will miss that the object is being controlled.
When tracking data such as public orbital element catalogs is openly published, an individual who continuously visualizes the whole dataset can catch a deviation before agencies that filter data through mission priorities and chains of approval. The advantage is not better sensors. It is attention to the full stream combined with a model of what normal looks like, so the outlier stands out.
Any system that can rendezvous with, push, or deorbit a piece of orbital junk can do the same to a working satellite or crewed station. Intent cannot be read from the hardware itself. So cleanup, commercial launch, and weapons programs become indistinguishable to outside observers, and whoever controls the software controls which one it is.