There are two chances of never again seeing the friends we part with when starting on a long voyage; those we leave may not be here on our return, and those who go may never come back. But little heed of these eventualities was taken by the sailors who were preparing for departure on board the Franklin in the morning of the 15th of March, 1875.
On that day the Franklin, Captain John Branican, was about to quit the port of San Diego, in California, on a voyage across the Northern Pacific.
A fine vessel of nine hundred tons was this Franklin — a barquentine fully canvased with gaff sails, jibs and stay-sails, and with topmast and top-gallant-mast on the fore.
1875 ends up being a hard year for the Captain John Branican and his wife Dolly Branican; while John is at sea, a tragic accident leads to the death of their son, Wat, and Dolly is thrown into such a state of shock at the lost that she loses her reason. She eventually recovers, several years later, but discovers when she comes out of her madness that John never came home -- the Franklin simply vanished without a trace. During her illness, however, Dolly had inherited a significant sum of money from an uncle, and so she puts it toward finding John, sending out a ship, the Dolly Hope, in order to find out what happened to the ship. The discovery of a lone survivor, who lets Dolly know that John was still alive when he last saw him, will send Mrs. Branican in an expedition across the dangerous country of Australia in order to rescue him before it is too late.
Mistress Branican (its title in both French and English), also occasionally known in English as the The Mystery of the Franklin, is pretty clearly a framework for Verne to engage in his taste for geographical fiction, in this case the geography of Australia. The framework story is interesting enough, but Verne doesn't do much with it beyond using it to get the characters moving on their Australian expedition. There is, however, an odd subplot about a man named Josh Merritt and his Chinese manservant who are engaged in a quixotic quest through extraordinary dangers to find a particular unique hat. This seems to be a case where this story grew up independently and Verne integrated it into a different story, not entirely successfully. A somewhat different version of Merritt's obsessive search for the hat, taking place in a different geographical context, seems to have been independently published in several newspapers. (Alternatively, it is possible that Verne himself was not satisfied with the handling in the novel and decided to rework it as an independent tale. I don't know enough about the background to say.)