The Secret of the Island by Jules Verne [Mysterious Island #3]

THE SECRET OF THE ISLAND is the third book in the 'Mysterious Island' trilogy (THE MYSTERIOUS ISLAND, and ABANDONED), and is related to 20,000 LEAGUES UNDER THE SEA and THE SEARCH FOR THE CASTAWAYS.

In THE SECRET OF THE ISLAND, A party of British ballooners have crashed on a remote Pacific island. There they must contend with both pirates and escaped convicts as they struggle to survive. However, as in the earlier 'Island' novels, they come to realize that someone or something is looking after them.