In the Bay of Naples lies a hidden wonder of the ancient world: Baiae. Three times as big as nearby Pompeii, Baiae was once an exclusive holiday retreat for Roman Emperors and the super-rich. With exclusive access to the work of underwater archaeologists and the help of a team of historians and volcanologists, this documentary investigates Baiae's ruins and artefacts to paint a picture of the ancient luxury resort, and explain how it became submerged. Rome's elite flocked here to enjoy the finest seafood and lavish beach parties, and to seek out love affairs amid its steaming sulphur baths. But they also came to scheme and plot against political rivals. Built in a volcanic landscape, Baiae's many villas and bathhouses took advantage of a constant supply of hot water, but the source of its popularity would ultimately seal its demise.