Previously, the party had stepped into the Feywild through a portal in the town of Moonstair. See, the town is right on the border of monster territory and has recently come under heavy, random assaults by various rogue monster bands. The nearby— metaplanary speaking, of course— Eladrin city had promised aid, but they themselves had come under seige from undead hordes.
On the way to the Eladrin city, the party had found The Garden of Graves, a once beautiful and tranquil Eladrin graveyard. The Garden had been savagely desecrated, and some sort of eldritch dungeon built out of the remains. This was obviously the source of the undead hordes.
The party then worked their way through the dungeon tomb— which seemed overly complicated and horror-filled— to its very heart where a magical device lay, drawing energy from the area and transporting it… somewhere else. This was destroyed.