NOVA takes a spellbinding voyage through one of the world's most fascinating and colorful ecosystems: a coral reef, where the line between plants and animals is blurred, "rocks" move, eat and fight, fish farm, and weak animals borrow the shields and weapons of stronger ones.

After receiving a warning from the White Guardian, the Doctor initially believes the TARDIS has landed aboard an Edwardian clipper ship - but all is not as it seems. While the time travellers are caught up in the omnipotent Eternals' race for the ultimate prize, the Black Guardian's scheme to destroy the Doctor enters the end-game - but which side is Turlough a pawn of?