The story of CS Mackay-Bennett, a cable repair ship launched on the Clyde in 1884. She kept information flowing along a network of underwater cables that connected Britain with her empire and the world - the Victorian internet of its day. It's also a story of a date with disaster, as the ship and her crew recovered the bodies of those who died when the Titanic sank. David travels to Halifax in Canada to find some facts about the ship and to unravel a DNA mystery that's taken over a century to solve.