In July 1909, the luxury liner SS Waratah disappeared off the volatile coast of South Africa with 211 people aboard, leaving no wreckage, no lifeboats, and no bodies. This episode traces the brief life of the ship called the Titanic of the South, the chilling premonitions that surrounded her final voyage, and the scientific theories of how a 465-foot steel vessel could simply cease to exist.

We examine her hybrid design as both luxury hotel and heavy freighter, and the dangerous top-heavy metacenter that gave her a slow, alarming roll. We cover passenger Claude Sawyer, who abandoned ship in Durban after a recurring nightmare and survived, and the disputed storm sightings before she vanished into a cyclone. We then weigh the explosion, rogue wave, and cargo liquefaction theories.

• Why a slow roll comforted passengers but terrified  ...