Viggo gets angry at the dragon riders continually interfering with his business and uses a deep sea dragon, the Submaripper, to control Berk's trade.

When the Eruptodon can't take its egg into the Great Volcano, Hiccup and Fishlegs must go into the dangerous volcano with the egg before it's too late.

Stoick and Hiccup are led on a wild goose chase in search of willow bark for medicine, leaving Berk vulnerable to an enemy attack.