Hiccup and Toothless return from a mission to find Berk mysteriously empty. They discover that the village has been overrun by Speed Stingers, a venomous non-flying dragon that has trekked across the frozen sea to Berk and driven everyone out of town. Hiccup must find a way to drive the Speed Stinger horde away from Berk.
One of the worst winters hits Berk and The Riders are forced to stay inside the Dragon Academy to avoid the blizzard. Hiccup tries to cheer up the Riders' spirits by teaching them some Dragon lessons, but they are not interested and not at all focused on Hiccup, due to the fact they've been stuck inside for a whole week straight and the others are starting to go crazy in order to keep them busy according to Astrid, (though she seemed to be paying more attention than the others). Barf and Belch chased their own tails out of boredom. And Ruffnut convinced her brother he had a tail, and Fishlegs was talking to Meatlug's toes. Stoick barely made it inside the Berk Dragon Training Academy, but freezing his beard frozen solid. Hiccup asks his father what brings him here, Stoick informs that Trader Johann hasn't reported to port for a long time now, considering the fact that he may be stuck and won't last long due to the weather. Hiccup, desperately wanting to leave, immediately volunteers to go and look for Trader Johann, to which Stoick agrees.
Along the way, Hiccup discovers that most of the sea has been frozen solid and figured out why Trader Johann cannot report to port. Also along their way, they barely see a herd of unknown dragon species. Hiccup is glad that they're only up in the sky and continues to find Johann. Hours later, Hiccup finally sees Johann ship, and gives Johann a ride on Toothless, forcing him to abandon his ship. While heading back home, Johann continues to tell hundreds of uninteresting and annoying stories that bothers Hiccup and Toothless all day and night.
As they arrive on Berk, they find most of the island mysteriously silent and empty. Hiccup also goes to the academy to check on the other riders but discovers that they are gone too. With no luck of finding any sign of life, Hiccup and Johann become suspicious, suddenly they see a moving figure inside a house and Hiccup and Toothless goes to check it out. Hiccup looks inside and gets pummeled by something heavy. He wakes up moments later, he sees Fishlegs and he is glad to see him, and begins to talk crazy mentioning the words speed and sting. Hiccup calms Fishlegs and asks what happened, Fishleg explains after nightfall the town was under attacked by Speed Stingers. A species of dragons that don't fly but moves into blazing speed and can paralyze a human or dragon with its stinging tail instantly. The Speed Stingers attacks in packs and follows a war-chief or leader that is identified with a red sail-fin on its head and appears much bigger than the rest. The residents of Berk are overwhelmed and flee out of town in disarray. Stoick orders them to evacuate to the cove and manage to hold out and buy some time for the people to flee, as soon as the area was clear the entire town have been overrun.
Fishlegs also tells them that the Speed Stingers exact location is unknown but he is sure that the Speed Stingers will return and scavenge for food again at night. Fishlegs refuses to leave Meatlug (who is paralyzed on top of their house). Hiccup and Johann are shocked that they missed that. As they try to get her to move, Meatlug farts in Johann's face and he falls down into a cart, but is okay. Fishlegs sees the farting as movement and concludes that the paralysis is only temporary. Fishlegs wonders how the Speed Stingers manage to travel to this island due to the fact they can't fly, Hiccup states that the Speed Stingers must have made their way to Berk after seeing a frozen bridge was formed earlier on in the ocean linking it to Berk. Meatlug is finally moved from the roof by Hiccup and Fishlegs. Unfortunately she falls in the same cart Johann is in.
Hiccup, Fishlegs and Johann make their way to the cove and see most of Berk's residents have been paralyzed, including Stoick. Gobber tells Hiccup that Stoick gave it all that it took 6 of the Speed Stingers to finally paralyze him. Hiccup regrets himself that he could've help Berk to defend against the Speed Stingers, but Gobber tells him to not be sorry, because they're were too many and it didn't matter if Hiccup come and help. Astrid happily greets Hiccup with a hug and is glad to see Hiccup okay and tells him that most of the riders are fine except for Snotlout, who got paralyzed by the Speed Stingers, while the Twins' continue to make fun of him. It's almost nightfall, and the Riders are worried that the Speed Stingers will return and finish off Berk's food supplies. Hiccup orders Astrid to assemble all the Dragon Riders and prepare for Hiccup's plan. Hiccup orders everyone to find out where are the Speed Stingers' nest are before nightfall dawns. They only have a few hours to find the nest. Suddenly, Snotlout wants to join in the mission, as his paralysis is beginning to wear off. But Astrid states that he can't go and ride Hookfang because his head is only doing movement. Instead, he orders Gustav Larson to help him move his arms and legs and tells Hiccup that he needs all the help he can get, Astrid and Hiccup reluctantly agree.
The actual plan is to find the Speed Stingers' leader and use it to lure them away. Most of the Riders find no luck of finding the Speed Stingers' nest. Hiccup asks the Riders again if they check every assigned cave given to each Rider, Snotlout gestures unnaturally after hearing that. Hiccup asks him if he checked his caves, but Snotlout doesn't admit the truth until Gustav tells him that Snotlout fell off Hookfang and spent hours trying to get him out of the sand. Hiccup now knows what cave to look, they rally close to the cave and bring in the cage. With only minutes away til' sundown, Hiccup and Fishlegs go inside the cave and finally find the Speed Stingers' leader, he traps him silently and Toothless stealthily grabs him. They drag him quietly to his cage but it's too late, nightfall has dawned and the Speed Stingers are beginning to wake up including the leader. Hiccup and Fishlegs hasten to drag it to the cage but the Speed Stinger breaks free and almost stings Hiccup, but Snotlout and Hookfang block the other Speed Stingers' only way out. However, while he cheers himself he gets stung again. Toothless tries to corner the Speed Stinger, but it orders its pack to desperately come and help him. Astrid and Hiccup attacks the Speed Stinger leader forcing him to fall back into the cage, his finally secured in the cage. As they try to pick up the caged Speed Stinger, the pack surrounds them in blazing speed unable to fly away. Stoick arrives just in time and Thornado blasts them away. Then Stoick faces the caged Speed Stinger in the eye asking him angrily if he remembers his face and what he did to him and orders the Riders to take him away off his island. Astrid grabs the cage and lures the entire pack of Speed Stingers' while Toothless provides cover.
One Speed Stinger jumps to the cage and stabs Stormfly, they crash into halfway of the frozen bridge. Hiccup volunteers to grab the cage while he orders the Twins to cover Astrid from the Speed Stingers. Some of the Speed Stingers fails to stop Toothless, but one stabs Toothless prosthetic tail, making them crash and they drop the cage and the Lead Stinger breaks free. Hiccup and Toothless are unable to defend themselves due to Hiccup's shield has used all of his bolas and Toothless has reached his shot limit. But luckily Snotlout arrives and blasts the ice bridge destroying the link to Berk. With the Speed Stingers unable to reach them, they are forced to turn back and search for a new homestead.
As the worst freeze in Berk disappears, most of the paralysis present is now gone and Berk's residents return to the village, as Stoick and Gobber repairs the damages. It's still revealed that Snotlout's paralysis hasn't worn off and the Twins and Gustav continue to make fun of him. Hiccup and Toothless with Trader Johann fly to his fixed and returned ship. To return the favor, Trader Johann offers Hiccup a bottle of large ink that he promised to give to Hiccup in the episode Dragon Flower. Hiccup thanks him and Johann tells him that there's actually a wonderful story that goes with it. Hiccup silently tells Toothless to go ahead and fly away from Johann, while Johann wonders where they are going. He hasn't finished his story yet and tries to convince them to stay. Hiccup just ignores Johann's story and the episode ends.
- The Speed Stinger makes its debut.
- First appearance of the Speed Stinger.
- In the previous episode Free Scauldy, Ruffnut cut her hair to save Scauldy, but it is now back to its original length.
- The numerous comments about the strangeness and severity of the freeze that hits Berk can also relate to Frozen, where the one of the main characters accidentally freezes an entire kingdom in the middle of summer.
- The episode's title is twofold. It not only relates to the way the speed stingers freeze their targets with their venom, but the strange freeze plaguing Berk during the episode.
- This is the first time Trader Johann is seen in Defenders of Berk.
- This is the first time Toothless has reached his shot limit.
- Counting the number of plasma blasts Toothless shot during the fight, which was about 14-15, it can be assumed that Night Furies reload quickly, since a Night Fury's shot limit is 6.
- This is also the first time Hiccup's shield has run out of bolas.
- At the end, Johann gives Hiccup a large bottle of ink from the colossal squid. This is a callback to when Johann said he would get Hiccup another bottle after Toothless accidentally broke it in Dragon Flower.
- This is also the first time Hookfang directly hurt a viking other than Snotlout (Tuffnut in the beginning).
- This is the fourth episode in the TV series to have a flashback.
- It is shown that Ruffnut has convinced Tuffnut he has an "invisible" tail.
- Snotlout is frozen for the majority of the episode with mostly only his head moving. When his body finally unfreezes, he is stung by the Lead Stinger, causing him to be paralyzed for the rest of the episode.
- Because Snotlout was paralyzed most of the time, Gustav had to substitute as Snotlout's arms and legs. Though Gustav showed some proficiency at riding Hookfang, Snotlout's body made it difficult for him to see and he even accidentally dropped Snolout's body a few times (though one time he purposefully pushed him.)
- If you look at the top of Fishlegs's house before Hiccup and Fishlegs reunite, Meatlug is nowhere to be found.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Nolan North as Stoick the Vast
- 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
- Michael Goldstrom as Trader Johan
- Lucas Grabeel as Gustav Larson
- Thomas F. Wilson as Bucket ♣
- ♣ designates a character that appears but does not speak