Stone-Age Companions

(Book 4) Anna Frost's powers grow more and more uncontrollable by the day. Meanwhile, Hiccup discovers his father is still disappointed in him. To make matters worse, North's portals to berserk and send the Companions back to the Stone Age! As everyone seems to enjoy the new time, Hiccup struggles, and for Anna, it seems like nobody can help her regain her once happy life.