Its 5th century Europeans vs.Norsemen in a tale following Hiccup&friends a year after establishing peace with dragons.The viking Chieftains have been called to gather. Worlds collide as Dragon, Jane, and their mysterious companion wash up on Berk's shores. One asking for peace, the other for blood.

I guess no one ever crossed over Jane and Hiccup because of the difference in Dragon mythology. But if some will turn Toothless Human than I can make him talk!