Captain Grant's Children by Jules Verne

A message in a bottle relays an urgent plea from the long-missing Captain Grant. His ship, the Britannia, has sunk. He is alive but is being held hostage. Captain Grant's children, Mary and Robert, along with their friend and benefactor Lord Glenervan launch a rescue expedition. But where do they begin their search? The original SOS message written in three languages is partially destroyed by sea water. The remaining fragments can be interpreted several ways. Only one clue is certain, Captain Grant is somewhere along the 37th parallel