Try working through a universe in which a young, growing Terran space effort (united? divided?) of maybe 40 systems and maybe 1-3 allied alien species bumps up against large, powerful alien empire, old, slow, patient, some tech advantage and some tech disadvantages. This empire should have a dominant alien race and several subject species. It isn't eager to enslave/destroy H. saps bu is driver to do so by obvious manifest destiny behavior on human part.
On other sides should be open/dangerous region(s), useful planets including undiscovered alien races, and maybe a smaller, but very aggressive alien territory or brushfire war neighbor.
Good king poisoned in ambush is resting up in Tower Keep in Wilderness awaiting rescue. An evil army joins the ambushers for assault to capture the king. A messenger has slipped away and summoned rescuers including a priest who can cure the king.
D&D room situation
An ornate room with frescos of the Walking Dead (skeletons, etc) in imitation of the Four Seasons.
Spring - planting, lovers wooing
Summer - peasants at fieldwork and nobles at war
Fall - Harvest festival, Nobles hawking
Winter - Feasting, Boar hunt in snow, skating
A tree carved of white marble stands in front of Spring bearing five ruby "fruits".
If PCs enter, five phantoms will materialize before them, somewhat slowly, taking one round, but can move while materializing. The phantoms are linked to the rubies. They attack by draining STR at 1D6/hit (recovered at 1/day if COM roll made)
They are 6 HD, AC 2, Move 9", invulnerable to normal weapons and dematerialized by magic weapons for # of rounds equal to hits inflicted.
They can pass through walls and doors an will stay within ten yards of the rubies, attacking if rubies are removed and carried on a D6 roll of 1 each combat round.
The phantoms can be destroyed by clerical turn as spectres. On turn result, they return in hours equal to the cleric's level. They can also be destroyed by magic weapons rolling an instant kill, 20 followed by 19-20 confirm, or a single hit by magic or a magic weapon over their HP, return in a number of days equal to HP. Or by destroying the gems.
They can be gotten rid of by leaving the gems.
A deep well shaft close to the room is a possibility.
A lawful cleric that inters the gems with a proper burial ceremony gets 500 exp, others 200 exp. If the rubies are interred with the crypts housing the final remains of the phantom's earthly bodies nearby, they achieve final rest and the cleric gains 1000 exp.
A Magic Mouth on the Door shouts when the door is listened to. "TRYING TO LISTEN TO THE DOOR, HUH?" "TRYING TO SURPRISE THE MONSTERS, HUH?"
Little man in little house -
A box like a gingerbread house, if handled, has a little man, 3" tall, come out.
He can be induced to serve in some way. When carried along, he'll leave box, shrink useful stuff to his size and take it into box. The box is like a little Tardis, has unlimited Dimension Door and will do so at his choosing or when threatened with damage, like attempts to pry or bash it open.