The Answer is: It is their only way out.
"Yes," replied the Professor, looking at me calmly from under his spectacles, "it is the only chance which remains to us of ever escaping from the interior of the earth to the light of day."
Irascible, irascible means to be easily angered.
I think metaphor because it is not something literal but it has meaning behind it.
A. unpleasant memories of Mary, who had burned protestants at the stake, remained
