How to Train Your Dragon Book 5 

In the fifth adventure in the How to Train Your Dragon series, someone has stolen the Fire-Stone. Now the volcano on Volcano Island has become active and the tremors are hatching the eggs of the Exterminator dragons! Can Hiccup return the Fire-Stone to the Volcano, stop the Volcano from erupting, and save the Tribes from being wiped out by the terrible sword-claws of the Exterminators?