How to Train Your Dragon #5: How to Twist a Dragon's Tale by Cressida Cowell

The heat is on for Hiccup as he is called to save the day once again. Someone has stolen the Fire-Stone. Now that the volcano on Volcano Island has become active, the tremors are hatching the eggs of the Exterminator dragons! Can Hiccup return the Fire-Stone to the Volcano, stop it from erupting, and save the Tribes from being wiped out by the terrible sword-claws of the Exterminators?