In a one-shot set months before the main campaign, three Undercroft workers — Barlow Crane, Grant FireEye, and Gage the Cunning — investigate sabotage aboard the massive moving Strider city of Iomenei. Tracking an elven suspect named Gerhardt into a long-abandoned forsaken sector, they discover an insectoid infestation centered on a dormant engine heart cathedral and must slay a massive Swarm Hive Mother. Though they halt the infestation, the true saboteur remains at large.