While Astrid, Snotlout and the rest of the gang are challenging each other to dragon races, Hiccup and Toothless journey through the skies, charting unmapped territories and exploring new worlds. When one of their adventures leads to the discovery of a secret ice cave that is home to hundreds of new wild dragons and the mysterious Dragon Rider, the two friends find themselves at the center of a battle to protect the peace.

Now chief and ruler of Berk alongside Astrid, Hiccup has created a gloriously chaotic dragon utopia. When the sudden appearance of female Light Fury coincides with the darkest threat their village has ever faced, Hiccup and Toothless must leave the only home they've known, and journey to a hidden world thought only to exist in myth. As their true destinies are revealed, dragon and rider will fight together-to the very ends of the Earth-to protect...