From publisher blurb:
Haunt of the Barrow King is a short Old School Essentials wilderness adventure for three to six characters of 1st-3rd level (about 10 levels total). The adventure involves a wilderness trek, an encounter with rival adventurers, and an undead menace. Haunt of the Barrow King contains a mixture of roleplaying, exploration, and combat. It takes place along a remote stretch of road and is designed to be dropped into any forested location.
Haunt of the Barrow King is an “event-based” adventure that is designed to be played in one or two sessions. It provides several opportunities for the characters to benefit from successful reaction rolls. This mechanic can be modified by various factors including good roleplaying, at the referee’s discretion. A number of different opposing factions (both living and undead) are present in Haunt of the Barrow King, so the referee is encouraged to read through the adventure and become familiar with their motivations and goals before starting the session.