W.H.G. Kingston & Jules Verne 
The Secret of the Island (Illustrated) [EPUB ebook] 

This book is a sequel to ‘Twenty Thousand Leagues Under The Sea’. A
party of British adventurers, who had been ballooning, but whose trip
had ended by being cast away on a Pacific island, have various setbacks
due to both pirates and convicts who had escaped from jails in mainland
Australasia. They realise that at times there appears to be some kind
of entity that is looking after them.
This entity proves to be none other than Captain Nemo whom the reader is
expected to have met before with his submarine ‘Nautilus’ in ’20, 000
Leagues’. Captain Nemo has been living in a huge cave inside the very
volcanic island, where he is surrounded with immense wealth. But he is
nearing the end of his life. We are present at his end. But what
happens after that is of great interest.