This episode includes footage of wildlife inhabiting underwater kelp forests, thousands of giant cuttlefish spawning along a restricted area of rocky reef off the south coast of Australia. Males outnumber females 11 to one, which leads to fierce competition. Larger males use brute force to drive off competition, while their smaller rivals use deception by mimicking the appearance of females. The programme also features tiger sharks hunting for green turtles in fields of seagrass and spider crabs trying to avoid predators while they shed their shells.

On the trail of tiger sharks in the Pacific, Will Smith explores the power of smell. Sharks have a sense of smell that's hundreds of times more potent and accurate than that of humans. An enormous part of their brain is dedicated to smelling, to finding their way through the vast expanse of the ocean.

As summer spreads across our planet, honey bees toil, snow geese breed, tadpoles awaken and lions stalk wildebeest in search of lush grass.
Our planet is solar-powered. But due to the Earth's tilt, it doesn't strike its surface evenly. This solar energy arrives in varying amounts at different times of the year. The huge increase that comes with summer also triggers countless migrations.