It's been ten years since the dragons moved to the Hidden World, and even though Toothless doesn't live in New Berk anymore, Hiccup continues the holiday traditions he once shared with his best friend. But the Vikings of New Berk were beginning to forget about their friendship with dragons. Hiccup, Astrid, and Gobber know just what to do to keep the dragons in the villagers' hearts. And across the sea, the dragons have a plan of their own...

When Hiccup and Toothless begin sharing stories of their special relationship with their respective families as they prepare for the Snoggletog Festival, it quickly becomes clear that the new generation of Vikings don’t remember the bond between dragon and human.

Jay and Gloria are navigating life with their youngest son, Joe, while Manny has headed off to college to explore the world on his own terms. Meanwhile, Claire and Phil have officially lost their status as empty-nesters when Haley started her own family and moved back home with her new husband, Dylan, and a set of twins. Luke, is now looking to his next move; and Alex is learning how to balance life outside of academia. Then there’s Mitchell and Cameron, who are still working to understand their gifted teenage daughter, Lily, and juggle busy careers.

As the tenth season kicks off, Jay's slated to be grand marshal in a Fourth of July parade, prompting the Pritchett-Dunphy-Tuckers to set off a few too many fireworks. Phil stumbles into a new career opportunity, while Claire grapples with her potentially changing role in the family. Meanwhile, Gloria obsesses over Manny's relationship and Joe's extracurricular activities. The extended family deals with death, but they also evolve, with more laughs than ever.

After his bachelor's degree is revoked, lawyer Jeff Winger returns to community college, where he forms a study group with a few oddballs.

The household hilarity continues as the Dunphy clan is wrapping up a Big Apple adventure. Back at home, Claire struggles to keep order at Pritchett's Closets while Phil and Jay go into business together. Gloria's hot sauce business heats up, as Cam and Mitchell deal with their maturing tween, Lily. Meanwhile, Manny and Luke fumble through their senior year of high school.