In 2017, Son Oh Gong and Ma Wang are in conflict with each other and they look for a true light in a dark world where evils exists everywhere.
The “Seven Deadly Sins”—a group of evil knights who conspired to overthrow the kingdom of Britannia—were said to have been eradicated by the Holy Knights, although some claim that they still live. Ten years later, the Holy Knights have staged a Coup d'état and assassinated the king, becoming the new, tyrannical rulers of the kingdom. Elizabeth, the king's only daughter, sets out on a journey to find the “Seven Deadly Sins,” and to enlist their help in taking back the kingdom.
When the Flyers try to kill him because he's no longer useful, Viggo forces Hiccup to help him get revenge by stealing their Dragon Eye and lenses.
After learning Krogan is using a Deathsong to lure and subdue Singetails for his growing army of Flyers, the Riders set out to rescue the dragon.
While on night patrol, Stoick is ambushed by the Flyers and gravely injured, leaving Hiccup torn between his duties as a son and as the Riders' leader.
After learning several Flyers followed Heather to Vanaheim, the Riders must stop them from reporting the sacred island's location to their leader.
With the fifth lens in place, the Dragon Eye 2 unveils the apparent King of Dragons, and Fishlegs immediately knows what it is and where to find it.
An announcement leads Astrid to question her relationship with Hiccup. The Riders discover an Armorwing that has a Dragon Eye lens welded to its body.
The Riders race to the home of the true King of Dragons. But the Flyers are already there, and they soon come face to face with the legendary creature.
While hunting for gemstones needed to complete the Dragon Eye 2, Hiccup learns an old friend isn't who he seems. Dagur faces a bully from his past.
While visiting Wingmaiden Island, a baby Razorwhip bonds with Ruffnut, who suddenly finds herself trying her hand at being a Wingmaiden.
Hiccup grows wary when Gruffnut arrives on the twins' 19th birthday to administer a Thorston coming-of-age ritual involving three dangerous challenges.
Upset after learning his ancestors were Hunters who killed off Dramillions, Fishlegs sets out to see if he can find any of the dragon species left.
Stoick and Hiccup are led on a wild goose chase in search of willow bark for medicine, leaving Berk vulnerable to an enemy attack.
During a trip to Wingmaiden Island to find a Dragon Eye lens, Snotlout challenges Hiccup's leadership. On another island, an unlikely romance blooms.
Sandi Toksvig ventures Overseas to find out about who keeps their brothers in a cage, and much more. With Bill Bailey, Colin Lane, Desiree Burch and Alan Davies.
Rodrigo distracts himself from the Requiem as he dives deeper into coaching Hailey for her big gig. Gloria gets a visit from a famous composer, eager to premiere his latest piece with the NY Symphony, but Thomas thinks his knows of a better fit. Despite doctor's orders, Cynthia returns to playing with renewed vigor.
On a mission to talk to Mozart, Rodrigo visits an unusual classical music collector (Michael Emerson) who might have what he needs. Hailey gets an exciting conducting opportunity, but has to prove she is up for the challenge. Thomas discovers the missing ingredient for the Queens Phil and invites Cynthia along for the ride.
Hailey faces off against new peers at the Fukusoft Conducting Competition in Japan. Rodrigo meets a new composer who claims to know more about Mozart than he does. Gloria tries to eclipse Betty in her fight for Fukumoto's attention, and Thomas is reluctantly reunited with an old flame.