D&D 5E - Espionage & Spies in D&D

So first off, no, I'm not talking about The Spy Game (a modern action espionage game by Black Cats Gaming that uses the 5E engine). It's a good game, but what I'm talking about is full-on fantasy D&D that focuses on espionage and spies. If you're not familiar with the genre and the tropes, here's a few links. Spy fiction and espionage tropes over on TVTropes. And just because, here's an educational link to the International Spy Museum.

For there to be a need for espionage and spies, there must be factions. I've got all that covered. The stuff I'm poking at with this thread is the use of existing D&D stuff for espionage purposes. Some obvious stuff jumps out like multiclassing rogue, proficiency and/or expertise in stealth, disguise kits, certain subclasses, certain races/lineages, etc. But there's a fair amount of stuff out there and I haven't read it all. Obviously things like scrying and disguises are important, as are preventing scrying and seeing through disguises. Zone of Truth to prevent lies. True Seeing to see through illusion magic. Sending or Sending Stones for long distance communications. Bag of Holding to covertly keep random bits of kit. Bag of Devouring to get rid of incriminating evidence. Amulet of Proof Against Detection and Location to avoid being scryed on. Changelings creating folds or flaps to covertly store items. Wildshape, polymorph, teleportation circles, and teleport for faster travel. Etc. Though I wouldn't want magic to the be end all be all of intrigue in a D&D game. Non-magical means of covert ops would be utilized as well.

To me, that's some of the obvious, low hanging fruit. So what are the harder to spot things that already exist in D&D 5E materials that could be repurposed for a D&D focused on espionage and spies? And if you were playing in an espionage and spies focused game of D&D what are the high points, tropes, and story elements you'd absolutely want to see?

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