The one key difference between Thyra and all the other Places, is (if one ignores magic, dragons, high technology, etc.), it that Thyra has NightGems, and the rest of the Multiverse does not. Why this is is a source of extensive debate, but the facts are there. This makes the city singularly important, not only as a hub, but also as the source of this material.
After the debacle of Passage 66, it became clear, throughout the Places, that all the eggs were very much in the same basket, and if Thyra fell, ALL the passages would be at risk.
TANDEM was created for this purpose. A rag-tag collection of individuals from all backgrounds, acting on an information network that extends throughout the Places. Not a fist, not even a scalpel, more like a snipers bullet, preventing situations from escalating, before they can endanger Thyra or its commerce.
With individuals and tactics from Places throughout the Multiverse, TANDEM are a force to be reckoned with. Moving in the shadows, and with absolutely no official standing, these people(s) have been key on keeping the trade going.
Secretly, that is.
Something I've been thinking about for some time. Perhaps having the characters have a bigger purpose, or indeed be a type of unofficial (and indeed illegal) secret agents, might open more doors to the narrative.