A pioneering marine biologist takes us down into the deep ocean to understand bioluminescence - the language of light that helps life communicate in the darkness - and what it tells us about the future of life on Earth.

Edith Widder's childhood dream of becoming a marine biologist was almost derailed during university, when complications from a surgery gone wrong caused temporary blindness. She became fascinated by the importance of light - as well as optimism.

As her vision cleared, Widder found the intersection of her two passions in oceanic bioluminescence, a little - explored scientific field within Earth's last great unknown frontier: the deep ocean. She leapt at the first opportunity to train as a submersible pilot and dove into the darkness.

Widder's first journey into the deep ocean, in a diving suit that resembled a suit of armour, took her to a depth of eight hundred feet. When she witnessed breathtaking underwater fireworks - explosions of bioluminescent activity - she only wanted to know one thing: Why was there so much light down there?

Below the Edge of Darkness takes readers deep into our planet's oceans as Widder pursues her questions about one of the most important and widely used forms of communication in nature. She reveals hidden worlds and a dazzling menagerie of behaviors and animals, from microbes to leviathans, many never before seen or, like the legendary giant squid, never before filmed in their deep - sea lairs. And we experience life - and - death equipment malfunctions and witness breakthroughs in technology and understanding, all set against a growing awareness of the deteriorating health of our largest and least understood ecosystem.

A thrilling adventure story as well as a scientific revelation, Below the Edge of Darkness reckons with the complicated and sometimes dangerous realities of exploration. Widder shows us how when we push our boundaries and expand our worlds, discovery and wonder follow. These are the ultimate keys to the ocean's salvation - and thus to our future on this planet.