Hiccup, Toothless and the dragon riders journey to Glacier Island in search of the Snow Wraith, a fearsome new dragon that holds the key to the Dragon Eye’s mysteries. 
Following the events of the previous episode, Hiccup must decide whether to save the still-trapped Riders on the quickly sinking ship or to stop Dagur the Deranged from escaping. He chooses to save his friends and letting Dagur sail off. The Dragon Riders are trapped within a cage made of dragon-proof bars, which prevent Toothless from blasting the lock open. Giant eels make their way towards them. Hiccup attempts to wedge the cage door open with his metal leg, and the door opens when the boat tilts. The Dragon Riders' dragons also return to them, saving them from the giant eels. Telling the Riders to head back to Berk, Hiccup flies off with Toothless to find Dagur and retrieve the cylinder looking thing.
After successfully retrieving the cylinder from Dagur, Hiccup returns it to Berk and names it the Dragon Eye. Gobber, to no success, attempts to open it. Only to find the Dragon Eye installed with multiple contraptions that shot Tuffnut with a sleeping dart, leaving him unconscious for a few seconds, as well as releasing a green gas that causes Tuffnut to have seizure-like jerking movements. Tuffnut is brought to Gothi for healing. A side-effect of Gothi's healing potion left Tuffnut's teeth itching, but it meant that the potion was working.
Gothi notices the Dragon Eye in Gobber's hand and turns pale. Hiccup asks her if she is okay, and she motions to the scar on her arm. It is shown to match the keyhole of the Dragon Eye. Gobber confirms to Fishlegs's comment about it looking like a dragon bite, but adds that Gothi doesn't like to talk about it. Convinced that whatever dragon's tooth caused the bite mark on Gothi's arm could be the key to opening the Dragon Eye, Gobber makes Gothi's favorite meal - Gobber's homemade yak noodle soup. Gothi finishes the meal quickly and tells Gobber and the Dragon Riders what had caused the scar.
Years ago, back when Gothi was still a teenager, she had a longing to climb Glacier Island to find pure glacier water known for its healing properties, so she went with two Vikings. They had only been at the summit for a few hours, when they were hit by a terrible snowstorm, and that's when they were attacked by a mysterious dragon that was impossible to see through the whiteout, vicious and relentless. The Vikings who accompanied Gothi were carried off and she came face to face with the dragon who was responsible. The Snow Wraith was ruthless and carried Gothi off by biting her arm, and dropped her into a snow pile. However, it never finished her off and walked away. Gothi eventually returned home with the knowing of never wanting to see that dragon again.
Realizing this is exactly what they needed, Hiccup tries to convince Gothi to go with them to the island, to find the Snow Wraith. Gothi at first refuses, and states that Berk needs her as she is the best healer they've got. Hiccup says that Gobber could take over while Gothi was gone. Hiccup changes Gothi's mind by having her relate to him, saying that the Dragon Eye would answer all the questions they haven't even asked yet, but only if Gothi helped unlock it. Moved, Gothi accepts and follows the Dragon Riders to Glacier Island.
On their way to Glacier Island, Fishlegs says that the Book of Dragons mentions the Snow Wraith, but did not have any information about it. Landing on the island, at first Gothi has nothing. Suddenly, a samll snowstorm covers the island. Astrid has the team spread out to cover more ground. Unbeknownst to them, the Snow Wraith was near them all along.
Back at Berk, Gobber is now temporary the village's healer. His first patient is Magnus. Magnus has his leg caught in an old dragon trap. Gobber heals him by taking off the trap roughly, and splashes an orange potion at the wound. Magnus screams in pain and claims that the potion had caused his leg to burn. Gobber cheerily states that it meant it was working, but to his surprise, Magnus' leg is actually on fire. Gobber fixes this problem by throwing a bucket of water at Magnus' foot. The bucket is flung away from Gobber's grip and knocks Magnus out cold. Gobber claims that he was cured and drags him away, moving onto the next patient.
At the Island, the snowstorm seemingly disapeers, and the Riders group together once again but none of them found anything. The twins only found scattered yak bones. While Fishelgs claimed that he did not see anything, although he felt like something was watching him. Another snowstorm approaches, this time a bigger one, and Astrid suggests that they should leave. Hiccup refuses and says that they should remain and wait until the Snow Wraith shows itself. He states that the dragon only likes to attack when you can't see it.
Gobber once again receives another injured Viking. This time, the Viking had stepped on a thorn. Gobber claims he could remove it quick, and the Viking is happy that Gobber could remove the thorn. However Gobber meant the entire foot itself, which sends the Viking running home. Leaving Gobber to stand alone, he states that "some people do not appreciate the practice of medicine".
The storm gets even worse, and Hiccup tells the Riders to use their dragons as extra protect from the wind. The Snow Wraith attacks, destroying their tents. They were told to hold their ground and fire back, but they could not see the dragon clearly. Realizing the danger they were in, Hiccup tells the Riders to take cover. The Snow Wraith fires a blast which sends Snotlout flying, landing in a snow pile. Hiccup gets covered in snow as well, and has a perfect view of the Snow Wraith.
The dragon heads over to the snow pile Snotlout was within, and sniffs around. However, it could not see Snotlout as it is revealed to have infrared vision similar to that of a snake. It could not see Snotlout due to the similar heat signature the snow pile and Snotlout has. Hiccup orders Toothless to fire a warning shot, which alerts the Snow Wraith of their position and it flies over. Hookfang and Stormfly also fire, which causes the Snow Wraith to head over to them instead. Hiccup and Toothless get out of the snow pile, and Toothless uses his echolocation power to locate the Snow Wraith from the whiteout. Successful, Toothless then releases multiple blasts, all of which it dodges. The Snow Wraith then retreats to the sky.
Snotlout gets impatient with Hiccup, pointing out his plan at getting the tooth from the Snow Wraith. Gothi tells the group that they should have left when they had the chance. The Snow Wraith howls in the distance, which causes the group to grow fearful.
At Berk, Agnar has a stomachache. Gobber claims that he has seen Gothi whip up a stomach cure a thousand times. He messes the recipe up, accidentally knocking in a green potion and sneezing into it two times. Agnar does not notice, so Gobber gives his medicine to him and tells him to drink it three times a day, and come back to see him if it doesn't kill him, to which Agnar is shocked to hear. Gobber reassures him that he is just joking.
On the Glacier, the Riders have a meeting. They are barely okay, and Fishlegs says that as much as he wants the tooth from the Snow Wraith as Hiccup, he understands the danger of being on the Island for too long, being sitting ducks in the storm. Hiccup is inspired by this, and with the knowledge of the Snow Wraith seeing heat signatures to target its victims, he comes up with a plan to confuse the dragon's sense. Although he is not sure if it would work.
They construct dummies from sticks and rags, positioned in a circle in the middle of a clearing. Assuming, the plan would be for the Snow Wraith to mistake the dummies as the Riders when they are lit up, then it would attack the figures, leaving it distracted from the real Riders. They would then have a drop on it. Toothless lights up the dummies and the Riders await for the Snow Wraith. At first it is quiet, but the Snow Wraith comes nevertheless. The Snow Wraith dives down and takes out Snotlout's statue, which he is quite fond of. Snotlout is peeved, so he orders Hookfang to flame up. The heat from Hookfang's fire melts the ice and snow from above, which sends the ceiling collapsing down onto the Riders. Toothless manages to save Hiccup from being trapped, but they are separated from the rest of the Riders and their dragons.
As the Riders attempt to get out, Hiccup and Toothless are vulnerable outside of the storm, with the Snow Wraith able to detect them easily with their body heat. They stay in the fire of the statues and Toothless uses his echolocation skill to locate the Snow Wraith from the storm. Toothless is unable to locate the dragon due to it avoiding it. The Snow Wraith sneaks up behind Toothless and Hiccup, but Gothi suddenly runs out to attack the Snow Wraith with her staff, fueled with anger from its previous attacks on her. Toothless blasts the Snow Wraith, and it lets go of Gothi's staff, which it had held onto. The dragon moves to attack Toothless and Hiccup, but Hookfang's blast drives it away. Snotlout exclaims that he is the one that got the remaining Riders out of the snow, to which Astrid responds that he was the one who got them buried in it to begin with.
Overwhelmed with the amount of dragons and surrounded, the Snow Wraith escapes from the Riders' clutches. Hiccup is upset that the dragon left without them getting the tooth from it. Astrid suggests that they should go, but Hiccup is determined to not return empty handed. While he is speaking, Gothi tries to get his attention. She interprets his monologue by showing him her staff, which has the Snow Wraith's tooth lodged on to it, from where it held on. Now in possession of what they came for, the Riders return to Berk.
Hiccup asks Gobber how it felt being Gothi for a day when they return, but Gobber is unable to complete his reply as Agnar comes running over. Agnar says that he must have more of the potion Gobber made him; while it didn't heal his stomach illness, it made Agnar's hair grow back. Gobber said it was just one of the side effects, and it is believed that diarrhea would be one of them as well. Gobber is unable to remake the potion of Agnar, so he changes the subject by handing the key, the tooth of the Snow Wraith, to Hiccup. Hiccup fits it in the keyhole, but nothing happens.
Perplexed, Hiccup decides to just call it quits after investigating the Eye late into the night, saying that he'll work on it tomorrow. Toothless gets ready for bed and heats up his sleeping slab; the fire from it is caught by the gem of the Dragon Eye, which is lit up and casts a hologram. Noticing this, Hiccup tells Toothless to hold a low flame. The light casts a stronger hologram onto the wall, revealing graphs of at least three different dragons. Hiccup claims that it changes everything.
- Savage still works for Dagur, and has shaven his mustache.
- This is the first time Gothi has a major role.
- Gothi's teenage self looks the same as she does, except with black hair and less wrinkles, interestingly even in the flashback she doesn't speak.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Chris Edgerly as Gobber the Belch
- Christopher Mintz-Plasse as Fishlegs Ingerman
- Andree Vermeulen as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson
- David Faustino as Dagur the Deranged
- Paul Rugg as Savage
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