HMHS Britannic was built as the third Olympic-class liner, Titanic's larger, supposedly safer sister, and this film traces how the outbreak of the First World War changed her fate before she ever carried a paying passenger. Converted into a hospital ship, Britannic ran medical evacuation routes through the Mediterranean until November 1916, when she struck a mine (or possibly a torpedo, the film weighs both) in the Kea Channel off Greece. The documentary reconstructs the sinking through survivor accounts and maritime historians, showing how design changes made after the Titanic disaster, watertight doors, davits, lifeboat capacity, still weren't enough to stop the ship from going down in under an hour. It also covers the chaos of two lifeboats drawn into the still-turning propellers, and the comparatively low death toll thanks to the crew's speed getting people off. The film treats Britannic as the overlooked third act of the Olympic-class story, less famous than Titanic but arguably a harder engineering puzzle to explain.