Luminous beings, creatures with their own internal light, enchant and astonish us. Anyone who has seen a firefly or glow-worm cannot help but fall under their spell. The sea at night sparkles, as millions of luminous plankton reveal the shapes of dolphins, fish and whales in a truly spectacular and magical light show. But why do animals produce living light? For centuries we could only marvel at the beauty and the mystery. Sir David Attenborough will be our guide as we venture into a new hitherto unseen world.