All aboooooaaaaaaaaard the
City Express!
...why yes, that's quite possibly in the cards again for our good citizens these days. But first, the other symptoms of the Omens Plot disease:
gravity goes haywire: small (mundane or relevant) items that fall on the ground seem almost drawn to the nearest drains, or holes, disappearing seemingly into thin air. It's entirely up to you whether citizens will be able to discover them in the depths of the underground, should they visit.
at night, residents will be able to hear odd sounds in their walls, as if creatures crawling down through them. Characters that sense auras or energy might be able to tell that the culprits are living entities, but not to determine their nature.
citizens travelling around the underground will find themselves drawn within it. It's up to you whether the thrall will hold only long enough to get them to the entrance, or farther.
following its recent revamp, the underground will greet its visitors with two changes:
o1. the 'sphinx'-hosting stone chamber has redecorated its graffiti gallery, which now prides multiple copies of the word EVIDENCE. The creatures within are somnolent and notably silent, and seem to be biding their time by building castles from sand, mold, and pebbles - then kicking them down.
o2. the City Express is still blocking its tunnel, but it has visibly moved, and access to the train is now possible through its conspicuously open doors. The Express lacks a formal staff, but once inside it, travelers might notice copies of a certain poster.
The GOOD: the Express can be started, and it's an interesting ride for all those willing to chance it.
The BAD: ...blood coin never seems to fall out of favour.
The UGLY: and it will take quite a bit of it to cover the trip.
The SAVING GRACE: it needn't be real blood. Smart citizens can always turn to alternatives: perhaps something in their canon that substitutes blood (be it in magical rites or symbolism), animal blood, chemical compounds - be inventive! (And let us know in the comments if you've figured out a way for your characters to get the Express started).
ACTION TIME: plans and plots in the comment section, go, go, go!