The Tickencote Treasure - William Le Queux

Paul Pickering is a doctor without a fixed practice, and when an old sea captain asks him to join a voyage around the Mediterranean, that's finally an exciting prospect for him. The journey goes well until they spot a most strange vessel somewhere off the coast of Algeria. It is an old Elizabethan craft that looks to have been submerged for hundreds of years and recently bubbled back up to the surface. The men board it and find that it had been hermetically sealed all these centuries, all contents intact. But it does not, as first hoped, contain gold. The men find barely legible manuscripts and a mysterious old man, who appears to be as old as the vessel itself... - Summary by Carolin