A quick recap of where we got to:
The party was contracted by the dwarf Gundren Rockseeker to deliver intact a cartload of provisions from Neverwinter to the town of Phandalin. Gundren claimed to have discovered "something big" near Phandalin and went ahead of the party.
On the way to Phandalin, with about one day's march remaining, the party was ambushed by goblins who were quickly dispatched. One goblin was taken prisoner and cruelly interrogated; he revealed the existence of