When Hiccup finds a coffin at sea, he opens it to discover a riddle that will lead to the treasure of Grimbeard the Ghastly, the world's greatest pirate and Hiccup's ancestor. So Hiccup and his friends set out on a treasure hunt, determined to master the art of swordfighting. How else will they escape an island of murderous dragons, defeat a boatload of Viking pirates, and survive all the twists and turns their journey will bring?