On the road to Phandalin, the party found a pair of dead horses blocking the road. On closer inspection, it was revealed that the horses belonged to Gundren Rockseeker and Sildar Hallwinter. Before the party could properly react to these revelations, they were ambushed by a group of goblins.
After the other goblins were dealt with the last one ran away. The party decided to give chase. They found goblin tracks, along with signs of two bodies having been dragged through that path. After evading some traps, they found the goblins’ lair, a cave northwest of the ambush site.
After fighting off some goblins, the party found their leader, a bugbear named Klarg. After a hard fight that tested the party to their limits, Klarg was slain. Examining that chamber of the cave, the party found stolen supplies from the Lionshield Coster, along with a chest belonging to Klarg, which was promptly looted.
The missing people are still to be found, but there is more of the cave to explore.