An unknown thief steals an important naval treaty from the office of Mr. Percy Phelps, a Foreign Office clerk. Phelps's distress gives him a brain fever that lasts for nine weeks. As he begins to recover, he writes to his old schoolmate, Dr. Watson, begging him to invite Sherlock Holmes to investigate the matter and find the treaty. Otherwise, his honor and happiness are gone forever. Holmes takes up the case with zest, but gives Phelps no false hopes. The mystery is as dark and tangled as any he has known.

叙述一位英国绅士Anthony Ross 爵士为了寻找失踪多年的儿子，于是他筹组了一支探险队展开行动，他的儿子当初是去寻找北极一带火山谷一个传说中的古老维京人部落，结果从此音讯全无，心急如焚的父亲因此才想尽办法组织探险队进行搜寻任务，这支队伍包括一位美国籍的考古学家、一位法籍发明家、一位追踪者以及英国企业家等等，当他们逼近目的地的时候，却意外闯入一个被时间遗忘的失落世界！这世界里有仍过着十世纪生活的维京人、火山爆发、鲸鱼墓场…等等，在这一连串的冒险当中，面对希望秘密永远被埋藏的那一群维京人，探险队面临到很难全身而退的危险局面！