Oldest Trick in the Book is one of the two-part missions assigned to Audrey Stolz to wipe out the cultists who banished Cassidy, Hugo's wife, in the Skyline Valley update for Fallout 76.

This mission consists of several parts, so we will explain everything you need to do to complete it in Fallout 76.

After completing the Seeking Shelter Skyline Valley quest, speak to Audrey in Dark Hollow Manor to begin this mission. During the conversation, Hugo Stolz asks for your help in finding his wife Cassidy. Audrey then tells you where Cassidy is and tasks you with finding her and exterminating the Cultist leader who captured her.

Once the conversation is over, a marker will appear on your map, indicating the location of the Old Crimora Mines in the southern corner of the map. Travel to the marked location and wipe out any Cultists roaming the surrounding areas.