Dragonryderdaguranderet cerita

when hicca (fem hiccup) runs away after being told that she gets to kill the monsters nightmere 6 years after she fakes her death the teens of berk + gobber and stoick are huntting for a new sorse of food and sume how find them selves outside the arcapeligo were thay are captured by a mistaryas female ryder and her 3 gang members. who is the misterias ryder? and how dose she know so much about the island of berk? and why is she so fermilia ?i