How to Train Your Dragon 2 Voices of Jay Baruchel, Gerard Butler, Cate Blanchett. Directed by Dean DeBlois. Rated PG. Opens Friday.

The plot of 2010’s How to Train Your Dragon was effectively simple: In a village full of dragon-killing warriors, shy, awkward Hiccup (voiced by Jay Baruchel) took a different path, befriending a dragon and ultimately proving that humans and dragons could co-exist peacefully. Having neatly resolved that issue, writer-director Dean DeBlois (who co-wrote and co-directed the first film) has a tough time coming up with a new story for How to Train Your Dragon 2. Instead of simplicity, the animated sequel opts for narrative clutter, with a number of different plot threads vying for attention.

There’s Hiccup’s burly dad (Gerard Butler) expecting his son to take over as the village’s chief; there’s an evil warlord (named Drago Bludvist, of course) building a dragon army; there’s Hiccup’s long-lost mother (Cate Blanchett) making her sudden return; and there are various bits of business with new and returning supporting characters. DeBlois builds on some of the first movie’s strengths, especially the inventive design for the dragons and the exhilarating flying scenes (which work well in 3D).

But the plot is unfocused and jumbled, borrowing elements from other fantasy movies without bringing them together into a cohesive whole. It’s also rather dark for a kids’ movie, with little of the first installment’s comic relief. At the same time, the serious moments lack gravity, making the story feel heavy but inconsequential. There’s enough roller-coaster-ride fun to keep fans engaged, but much of the charm and emotional resonance is missing.