Helen joins Chalke Valley History Festival to talk about her brand new book Blue Machine – How the Ocean Shapes our World. Diving deep to illuminate the murky depths of the ocean, she examines the messengers, passengers and voyagers that live in it, travel over it, and survive because of it. From the ancient Polynesians who navigated the Pacific by reading the waves to permanent residents of the deep such as the Greenland shark that can live for hundreds of years, she will explain the vast currents, invisible ocean walls and underwater waterfalls that all have their place in the ocean's complex, interlinked system.

Venue: Evelyn Partners Tent, Broad Chalke, Nr Salisbury. Start time: 7:30pm.