Fill in the blank: From the Chateau D'If we hear the sound of an explosion. It was the alarm cannon It means that... (17)

.... a prisoner escaped

A small white cloud, which had attracted Dantès’ attention, crowned the summit of the bastion of the Château d’If. At the same moment the faint report of a gun was heard. The sailors looked at one another.

“What is this?” asked the captain.

“A prisoner has escaped from the Château d’If, and they are firing the alarm gun,” replied Dantès.