A mystery typically lasts 1-3 sessions and follows a structure: (1) Preparation in Upsala - gather information, buy equipment, gain Advantages; (2) Invitation - learn of a problem in a remote location; (3) Investigation - visit locations, interview NPCs, collect clues; (4) Escalation - the situation worsens and secrets reveal themselves; (5) Confrontation - face the vaesen or its controller; (6) Resolution - banish the creature and return home to recover.
Mysteries are solved through gathering and piecing together clues. Investigation tests reveal clues in locations. Observation tests help you notice details about NPCs. Learning tests let you understand old texts and folklore. Speaking with villagers, examining crime scenes, and consulting old records all provide pieces of the puzzle. The Game Master presents information through these interactions, and your careful detective work reveals the truth.
There's rarely one 'correct' way to solve a mystery. You might talk your way into information, break into a building, persuade an NPC to betray their secret, or find evidence through careful investigation. Your choices matter. If you visit an NPC the mystery didn't expect, the Game Master adapts. If you choose to confront the vaesen early, that's your choice - but you might not have enough information to win. The story adapts to your decisions.