The Longest Day is the seventh episode of Dragons: Race to the Edge, Season 4. It was released on Netflix on February 17, 2017. The name of episode was first revealed in the Everything Geek Podcast Interview with Douglas Sloan and Art Brown.
During the week of the Midnight Sun where the sun doesn't set for two weeks, Hiccup must deal with sleep deprivation and a dangerous new dragon. 
In an island somewhere, a few dragon hunters hear a loud distress from an unknown dragon, the hunters decide to check it out and deliver it to Viggo but once they come close to it, they are suddenly attacked by an unknown creature.
On Berk, Stoick is admiring night 8 of the Midnight Sun, where for two weeks the archipelago will experience constant sunlight, as the villagers work to recover after the crisis with the trade ships. But Gobber tells Hiccup that with no sleep for an entire week, people will start experiencing the effects of sleep deprivation. Hiccup assures Gobber that the Riders are assigned to do the simplest task of washing their dragons, in order to prevent them from getting too tired and succumb to the effects.
On the Edge, however, the Riders have been trying to bathe their dragons to no avail due to insomnia, Heather is experiencing lack of coordination, Astrid with uncontrollable euphoria, and Snotlout with mood swings. The Twins, not yet succumbing to sleep deprivation, are observing the Riders for their own amusement as they succumb to the disorder, being expert at naming the symptoms after their uncle had insomnia for 27 years, and almost able to predict Fishlegs' symptom of having paranoia.
Hiccup and Stoick are having dinner at their household, Hiccup then asks Stoick permission to borrow the Auxiliary Riders for a quick inspection but Stoick knows that he's lying. Stoick then reveals for him his true intentions, to seek revenge at Viggo and reclaim the Dragon Eye. Hiccup tries to reason with Stoick that Viggo is a threat to Berk and the dragons, but Stoick tells him that seeking revenge will be pointless and that he needs to come up with a plan first before taking action, Hiccup then leaves while Tootless follows.
While flying, Hiccup lets out his frustration on his father at Toothless but then they hear a dragon in distress from an island. As they inspect the shores, they find the remains of Dragon Hunter equipment and also discover the dragon calling for help. As Hiccup tries to inspect the unknown dragon's injury, three other dragons of the same species ambushes them, realizing the dragon was luring them to a trap. Fortunately, Toothless manages to fend of all four of them and they retreat. Hiccup decides to go deeper in the island much to Toothless's reluctance.
Meanwhile, the Riders continue to be paranoid with each other while their dragons look on. The Twins watch in amusement but they then forge a competition on which one of them will succumb to insomnia first, where both boast that they could stay awake and sane for weeks.
Hiccup and Toothless then stumbles upon a tight canyon, they decided to go around it but are then faced with the hostile dragons launching fireballs that can spread like lava or explode on impact. Hiccup and Toothless are forced to fall back inside the canyon, as the hostile dragons close in, HIccup tries to dissuade them not to attack by showing his fire sword but fails. Toothless attacks and causes rocks to tumble down and block one side of the canyon.
On the Edge, the dragons watch uncomfortably as their riders continue to act insane, including the Twins, who have now begun to show symptoms of insomnia but won't admit that one of them is actually experiencing the effects.
Back at the island, Hiccup and Toothless continue to be led deeper into the island as the unknown dragons continue to assault them. The duo face a dead end and see more Dragon Hunter equipment, Hiccup suspects that the hunters were the one 'hunted'. Hiccup then finds an opening and immediately rides Toothless to fly out and escape. Once in the air, however, the hostile dragons are facing them but suddenly dives down into the forest. Hiccup is confused, but an even bigger unknown green dragon emerges behind them and lets out a huge deafening roar at them. This turns out to be the signal for the numerous smaller unknown dragons to gather and cling onto their leader's wings, and this makes the big green dragon fly while the smaller dragons fires a huge barrage of exploding fireballs at Hiccup and Toothless. Unable to dodge all, Hiccup and Toothless are both shot out of the air and crash lands back down the island.
Hiccup and Toothless run for cover, where they find a cave that houses a now-abandoned Dragon Hunter observation post. Hiccup realizes that this is where the hunters' keep an eye on Berk, but had to evacuate immediately after the unknown hostile dragons came. As Hiccup tries to think of a plan to escape, he names the large hostile dragon Shadow Wing (the small ones are later known as Small Shadows). At first Hiccup struggles to come up one, but when Toothless sneezes at the map, Hiccup comes up with an idea thanks to Toothless.
At the Edge, the conditions of the Riders' worsen and both Tuffnut and Ruffnut had fully succumb to insomnia without realizing it. Having enough, the dragons grab their insane and sleep deprived riders and drop them all into a dark underground hatch under the arena.
Meanwhile, Hiccup sets his plan in motion by first innocently drinking water near a lake, two Small Shadows think that Hiccup is alone, but the moment they charge forward they get trapped by a Hunter dragon net set up by Hiccup. Four more Small Shadows pursuit Hiccup inside the observation post, but they are then fooled by a dummy inside the main room. Hiccup then orders Toothless to shoot down the entrance and trap the four Small Shadows inside. They set flight to face the remaining four Small Shadows and the Shadow Wing, Toothless manages to shoot down two Small Shadows at one side of the Shadow Wing's wing. The Shadow Wing then counters by whacking Toothless with its tail, and the remaining Small Shadows latches on Toothless's wings to slow them down. With the Shadow Wing coming closer, Hiccup has little time to come up with an idea but Toothless beats him to it, by suddenly diving down towards the lake, doing a barrel roll that throws the two Small Shadows off of his wings, shoots multiple plasma blasts at the lake that creates a thick fog, and then uses his echolocation to know the right time when to go back up in the air. With the fog offering little visibility, the Shadow Wing crashes down at the lake. With a successful evasion, the duo then fly back to the Edge.
As they land at the arena, Hiccup finds that the dragons are not washed and discovers the Riders sleeping down a hatch under the arena's floors. Hiccup points out that they get to sleep but not him, but Toothless suddenly pushes him down. With the darkness enveloping them inside, Hiccup quickly falls asleep as do the dragons after a long day.
The transcript for this episode is here
- The way Hiccup and Toothless defeated the Shadow Wing is similar to how they defeated the Red Death.
- The insomnia has different effects on the characters:
- Hiccup loses the ability to think properly.
- He even forgets how to fly Toothless momentarily.
- Astrid "enjoys" uncontrollable euphoria.
- Fishlegs suffers acute paranoia.
- Snotlout suffers severe mood swings.
- Tuffnut suffers hallucinations.
- Ruffnut becomes schizophrenic.
- Heather suffers lack of coordination.
- Stoick loses focus easily.
- Gothi "babbles", a lot.
- Silent Sven dances with all his sheep.
- Hiccup loses the ability to think properly.
- Astrid's behavior when she had insomnia is similar to that of Joy from Inside Out movie.
- When Stoick say "You're a terrible liar" to Hiccup, it's a reference to David Stutler from Sorcerer's Apprentice who potrayed by Jay Baruchel.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Christopher Mintz-Plasse as Fishlegs Ingerman
- Zack Pearlman as Snotlout Jorgenson
- Andree Vermeulen as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Mae Whitman as Heather
- Nolan North as Stoick the Vast
- Chris Edgerly as Gobber the Belch