From the PDF introduction:
Many years ago two large armies fought over a long lost cause. A brave knight who fell in the combat was buried in a lavish tomb. Over the years, the nearby swamp spread over and conquered the tomb. The knight's spirit protects the area and the nearby village. His name was Darius but none remembers it, yet for years the villagers regularly brought a tribute of flowers to his grave, in his honor. As the years passed, this custom waned.
Last month, a tribe of goblins moved into the swamp. This infuriated the knight's spirit, which in turn cursed the villagers. The villagers turn to the PCs for help, asking them to venture into the tomb and place a flower bouquet over the knight's grave, deep inside his tomb. The tomb has half-sunken into the swamp floor, and its two side wings are mostly underground. The floor is dirty and there are several holes in the ceilings.