Just finished a short session in which the party is hired to deliver a "precious" package.
Upon picking up the delivery the party encounter resistance in the form of a rival gang. The package is a "baby". The party does not know who the baby belongs to. (My group decided it was a bastard child of one of the noble families) I provide instructions after each encounter if the form of sealed messages that the party must break in order to get the additional information. Thus adding to the covert nature of the objective.
Once the baby is in their possession strange things begin to happen, visions, feeling of betrayal, being attack by an insect swarm.
Final instructions are to deliver the baby to a healer outside of town. The healer and her two mange ridden dogs turn out to be a Tzeentch sorceror and the dogs a couple of demons. The baby is born with the mark of Tzeentch.
The party eventually killed the demons, but is now burdened with a dilemma. What to do with this baby. Do they kill it? Find out where it came from? Turn it over to the authorities? Try to save it? And that's where we left it.
I should probably write it up. It's more than a one page adventure, but it went really well. Used a bunch of handouts and notes to create confusion and party tension as the baby begins to corrupt the party. Also, my first opportunity to roll for corruption.
A bit of Call of Cthulhu thrown in.