The Entangled

When I think about something that is ancient, mysterious, incorporeal and connected to espionage, I think the most fitting idea would be:
Quantum Entanglement!

I can go a bit into depth of the thoughts behind this:

In quantum entanglement, two particles are made to interact in a way that entangles them: They form a single (quantum) state together, no matter how far the particles are seperated from each other. The state itself is more than just the two particles blatantly combined - it's the special kind of interaction, the entanglement, that makes up its reality. The biggest part of a quantum entangled state is without matter or form, and can just barely be described by more or less complex math. 

Imagine being a quantum entangled being for a second. Your matter could be spread all over the milky way, but you wouldn't lose your sense of self. 

And of course, quantum entanglement will play a giant role in human espionage, since, while it is basically useless for sending information (due to various restraints), it is insanely useful for creating virtually indecipherable encryptions!