From the introduction:
The Ghost Tribe of Orcs have been driven from their home under Wyvern Tor by some terrible evil and have traveled to the top of the hill overlooking Phandalin where they camped last night. Their chief, driven mad by unknown horrors, prepares to attack the city and claim it as his new home. The heroes, who raced to the town ahead of the orc tribe, spend the night helping to prepare defenses and rest when they can.
Can the heroes help defend the town or will the orcs wipe out the inhabitants of Phandalin?
A 2-4 hour adventure for 5th-6th level characters.
Requires the use of the Unearthed Arcana "Mass Combat" optional rules.