The Viking Claw, 4

Finn and his mystery-writer uncle head to Iceland in search of the Haunted City of Tquuli, where Finn’s archaeologist parents were last seen before their odd disappearance eight years ago. Finn doesn’t believe the creepy legends about the Haunted City and the ancient Vikings who lived there — until a member of the rock-climbing expedition vanishes from inside a sleeping bag…one that was dangling a hundred feet from the base of an icy cliff

Then another climber disappears, leaving a trail of footprints that abruptly end in a field of snow. Is it modern-day murder, or the revenge of phantom Viking warriors?