Thinking he's allergic to his best friend Meatlug, Fishlegs gets hypnotized – and wakes up transformed into an invincible warrior known as Thor Bonecrusher.

As a Rumblehorn dragon wreaks havoc on Dragon's Edge, Hiccup seeks the help of Stoick – who forms an unexpected bond with the rampaging beast.

The dragon riders are surprised to discover who is behind recent attacks on nearby ships – and to learn exactly what the ships are.

A familiar face joins ranks with the dragon riders, but it's not an easy alliance, especially when Hiccup uncovers a shocking secret about the new member's true identity.

Hiccup, Toothless and the dragon riders rescue a wounded Speed Stinger and take it back to Dragon's Edge, unaware of the dangers that follow.