When the town's well runs dry, Hiccup and Toothless discover a group of baby Whispering Death dragons living in the tunnels underneath, planted there by Alvin.
Stoick, Hiccup, and Astrid are trying to corner an uncooperative Gobber in order for him to bathe, as he hasn't bathed for weeks. They finally surround him, while Fishlegs lifts the bucket of water in order to fill the tub with water. Snotlout and Hookfang appear from behind Gobber. Snotlout orders Hookfang to toss him into the tub, but instead he tosses his rider. Toothless sneaks from behind Gobber; while Hiccup signals Astrid, it distracts Gobber giving Toothless the advantage, and finally tosses him into the tub. Stoick holds him in case he tries to escape. Fishlegs and Meatlug arrive to drop the bucket filled with water, but they reveal that the well has run dry as they only manage to get a few drops. Stoick becomes suspicious.
Hiccup and Stoick discovers that the well has gone dry, but it seems impossible to be empty now as they just dug and filled the deep well two summers ago. Stoick just orders the Riders to build a new well, until then they have to ration water, meaning Gobber is free of having to bathe.
At the Academy, While a new well is being dug, Hiccup orders the Twins to get water from Lars Lake. Snotlout and Astrid are ordered to fill the water canteens from the water streams at the Cove. Fishlegs and Meatlug are assigned to help Hiccup figure out why the well quickly ran dry. Meanwhile, at the Cove, Snotlout plans to instead sell the water in order for him to make a fortune. Astrid is reluctant and does not approve of Snotlout's plan, but Snotlout decides to sell the water himself. Meanwhile, at the town's empty well, Meatlug flying overhead lowers Hiccup down the well. Hiccup discovers that the water level was far from dry and empty, as the walls are still wet, but somehow it disappeared. Hiccup throws a rock down to check if there's any more water, but hears no splash. He orders Fishlegs to tell Meatlug, to lower him all the way down. Toothless is noticeably worried for his Rider. While he is being lowered gently, Meatlug spots a pile of rocks and suddenly changes her mind and decides to eat them. The pulling of the rope disorients Hiccup and suddenly it snaps causing Hiccup to fall down the well. Toothless quickly goes after him, leaving Fishlegs to worry about what would happen.
Hiccup crashes down into a cavern along with Toothless, but they are both fine. Stoick calls for his son, Hiccup responds that he's okay, but Stoick wants to come down and help him get up. Hiccup tells his father to not do so, otherwise all three of them will be stuck. Hiccup instead goes on to explore the cavern and investigate where the water had gone. They quickly discover a tunnel, and decide to explore where it leads. Hiccup already has a feeling that they're not alone and Toothless hears brief noises but continues to explore the tunnel. They find themselves inside another cavern, where they spot dozens of hatched Whispering Death eggs. They also spot a crate that has the Outcast symbol imprinted on it, and spot a very large tunnel that was last seen in the episode The Iron Gronckle.
Meanwhile, Snotlout selfishly sells the water canteens to innocent 'thirsty' vikings. Astrid is still reluctant of Snotlout's plan, and even steals one of his water canteens and tosses it to some of the vikings for free. Hiccup and Toothless try to find a way out but discover that it is blocked by many rocks. Suddenly Hiccup's lantern goes off for a brief moment, and once they put it on again a Whispering Death startles Hiccup. Toothless quickly fires a plasma blast at it. They quickly flee to find a way out of the caverns, but two more Whispering Deaths join the pursuit. As they fly off, the three Whispering Deaths suddenly dissapear. They go back to investigate and discover that they are going instead to the surface and wreak havoc. Hiccup and Toothless must stop them before they cause absolute chaos.
Back on Berk, While Snotlout keeps selfishly selling water, Gustav Larson feels the earth shaking and becomes suspicious. The shaking grows violently and a Whispering Death emerges in front of Gustav. The Whispering Death fires. Luckily, Gobber appears to try to fend it off while Gustav escapes. The Whispering Death burrows underneath and throws off Snotlout's profits and water canteens. Within minutes, the Whispering Deaths emerge and begin their onslaught. Stoick signals the vikings with a loud horn, and gives it to a Viking who he orders to keep blowing. Stoick orders the Vikings to form a defensive line in the middle of the town. Snotlout runs for his life while a burrowing Whispering Death is in pursuit. He almost gets caught but is rescued by Hookfang. Astrid and Stormfly arrive to fend off the Whispering Death in pursuit of Snotlout and Hookfang. Fishlegs and Meatlug defeat a Whispering Death who is about to attack Astrid and Stormfly from behind. Stoick is surrounded by the 3 Whispering Deaths and he only manage to stop two, the third one is about to finish him but Stoick quickly grabs a wooden umbrella and shoves it into its mouth. He gets dragged and tossed at Gobber, knocking him down. The Vikings are overwhelmed at all sides, Stoick orders Gobber to be in charge as he runs for Thornado. Astrid asks Fishlegs about where these Whispering Deaths came from and to why they're so much smaller than average. Fishlegs replies that the Whispering Deaths are just hatchlings, meaning to say they're more deadly and dangerous as they do not yet control their jaw muscles and spines properly and can be compared to 'out of control saw blades'.
Meanwhile, Hiccup and Toothless navigate their way out of the tunnels, thanks to Toothless' ability to see in the dark. As they emerge, they discover that the village is under attack. Astrid and Stormfly informs the Twins that they can fight the Whispering Deaths better if they're above ground, but the Twins' are just observing their destructive behaviour, it serving as entertainment for themselves. A Whispering Death attacks them from behind and Barf sprays gas at the Whispering Death. Meanwhile, Snotlout and Hookfang flush out the Whispering Death by bursting the tunnels into flames forcing them to come out. Hiccup heads for Gobber's workshop and orders Toothless to provide cover while he retrieves his shield. A juvenile Whispering Death spots Toothless, and they attack each other brutally. It looks like Toothless would lose the confrontation, but luckily Hiccup's shield reflects sunlight into the Whispering Death's sensitive eyes and it gets disoriented and flees, remembering the Whispering Deaths' weakness. Hiccup informs Astrid that the Whispering Deaths were the ones who drained the town's well, but she is already aware of this fact. To keep them away from town, Hiccup reflects sunlight onto the Whispering Deaths with his shield and chases them away. Snotlout and Hookfang also drive them off by shooting a fireball at them. They reach the far side of the island and the Whispering Deaths seemingly flee from the island, though the twins miss them. But Hiccup feels it's not over.
As soon as he said this, the island shakes more violently this time, and a huge White Dragon emerges and attacks one of the Riders. It tears through the village, destroying anything in its path and drills into the ground beneath it. Fishlegs informs Hiccup that he has never seen a Boulder Class or Titan Wing dragon like that before. Hiccup and Toothless tries to get its attention by firing a plasma blast, the White Dragon grows furious and emits a loud scream that disorients nearby dragons. Tuffnut comes up with the official name for the dragon, The Screaming Death, and seems to love it. Then, the Whispering Deaths quickly come to the Screaming Death's aid, and Tuffnut is less eager to praise it.
Hiccup orders the Riders to fend off the Whispering Deaths and he himself will deal with the Screaming Death. The Screaming Death begins its rampage and startles a Viking lady, luckily Hiccup and Toothless fend it off but get whacked by its tail, and they crash into the ground. The Screaming Death is about to attack them, but suddenly gets blasted by Stoick and Thornado, who finally arrive. Hiccup and Toothless regain to fly again, and set off to get it out of the village while Stoick and Thornado follow.
Meanwhile, Astrid and Snotlout who are being followed by a Whispering Death, split up and Snotlout seperates from Astrid. The Whispering Death follows Astrid and Stormfly, who try to evade the Whispering Death. Just ahead of their path, Hookfang bends a tree and waits for Astrid and Stormfly to pass by, as soon as they do, Hookfang lets go and the Whispering Death gets battered by the tree. The Whispering Death flees. Meanwhile, Fishlegs and Meatlug wait for the perfect moment for the to attack the Whispering Death. The Whispering Death closes in but gets farted on by Meatlug. It makes the dragon angry, but it gets whacked by Meatlug's tail bludgeon and plummets into the ocean.
Back on Berk, Hiccup and Toothless try to fend off the Screaming Death by using the Whispering Death's weakness of being blinded by sunlight. It seems as though the Screaming Death hates it too and burrows underground, but only for a brief moment. It becomes angrier and quickly emerges and shoots between Stoick and Hiccup, even though it's still being shined on by sunlight. The Screaming Death screams again and disorients Toothless and Thornado, Toothless fires a plasma blast to shut him up. The Screaming Death chases Hiccup and Toothless towards sea, and Stoick flies for help, but gets blocked by a Whispering Death. He fends it off with a sonic blast. As soon as the Whispering Death falls back to the ground it gets blasted by the Twins, who are ordered by Stoick to find and help Hiccup. Meanwhile, Hiccup tries to shine some light again onto the Screaming Death's face and discovers that it is attracted to sunlight, and uses it as an advantage, he diverts it to the sea stacks while the Riders follow him from behind. Astrid and Stormfly quickly manage to catch up with Hiccup and Toothless. The two seperate, but the Screaming Death manages to force Hiccup and Toothless to land. The Riders attack it ruthlessly, providing covering fire for Hiccup, but the Screaming Death fires multiple fire balls to fend off the Riders. Hiccup tries to get its attention by attracting it to his shield which reflects the sunlight onto the great dragon. They use evasive manoeuvres, darting through the sea stacks. Hiccup discovers that he can use its own size against it. The Screaming Death crashes through all the incoming pillars of rocks. Hiccup and Toothless stop for a moment near a large pillar and the Screaming Death dives in towards them quickly, but they manage to fly upwards and the Screaming Death hits the pillar hard and painfully, and it is finally stopped.
The pillar it bumped is beginning to collapse and giant boulders crash into its wings, injuring it and making it unable to fly properly. It calls for the Whispering Deaths, signalling that he needs help. The Screaming Death tries to fly off, but it can't, and it crashes down the cliff and onto the platform beneath it. The Riders observe this, and they also see the Whispering Deaths aid the Screaming Death, and they fly off in retreat. Toothless wants to finish them off, but Hiccup decides to let him go and the Whispering Deaths and the Screaming Death fly off for a new homestead.
Back on Berk, the Vikings repair the damages done to the village. Hiccup informs Stoick that the Outcasts were the ones responsible for planting Whispering Death eggs beneath Berk and would soon hatch to tear Berk apart, he suspects that the Outcasts might not be riding dragons yet, but they are using them. Stoick tells him to deal with the Outcasts later as they focus more on how they are going to fix the town's water problem. Fishlegs calls them and informs that the old town's well is being filled with water again, Hiccup figures out that the Whispering Death's mass tunnelling must have created a new channel for water to redirect it up to the well, refilling it again. Which means that the Vikings may return to the original problem - forcing Gobber to have a bath.
Meanwhile, Astrid asks Hiccup what he is so worried about, since the Screaming Death is presumably finally gone. Hiccup informs Astrid that Whispering Death hatchlings are known to return to their birthplace and claim it as their own, no matter at what cost, meaning also that the Screaming Death will one day return.
On a far island, which is now the temporary rest stop for the Whispering Deaths and the Screaming Death, the Whispering Deaths gather fish for the Screaming Death who is resting its injured wing, so that it will one day return for its revenge on Berk.
- The Whispering Deaths are about the same size as the adult that Toothless battled, and the adult that Alvin bonded with, despite Astrid calling them "much smaller".
- There is no sunlight for Hiccup's shield to reflect light off of because it's cloudy.
- In dragonpidia, a picture shows a Screaming Death that is missing the claws on his left wing.
- Despite dozens of eggs being placed under Berk, only three Whispering Deaths appear.
- According to Hiccup, the Outcasts haven't learned to ride dragons yet, but they are using them.
- Hiccup confirms Whispering Deaths aren't "one of his favorite dragons."
- It is revealed in this episode that Gobber doesn't like to take baths, like his book counterpart.
- An episode of Pokémon happened to have the same name, and featured a group of Onix. Like the Whispering Death, Onix' resemble large, underground dwelling snakes.
- Fishlegs and Meatlug have claustrophobia, the fear of tight spaces.
- Or so Fishlegs claims. He might have just been trying to get out of helping.
- The line of people Gobber gives water to out of a trough is composed of one man and one woman copied and pasted multiple times, with minor clothing changes.
- The two men Astrid throws water to were missing only moments before.
- Thunderdrums are supposed to be hard of hearing, yet even Thornado is affected by the Screaming Death's scream.
- Tuffnut and Ruffnut missed the class where they trained against Whispering Deaths.
- Juvenile Whispering Deaths don't have control of their jaw muscles or their spines.
- Fishlegs compares them to out of control saw blades.
- 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
- David Tennant as Spitelout Jorgenson ♣
- ♣ designates a character that appears but does not speak