Dr Chris van Tulleken, Dr Hannah Fry and Michael Mosley examine the latest research and explore some of the big questions about Covid-19 and the pandemic it has created. Michael visits the UK government's high-security laboratory Porton Down, where vaccines are being tested. He also uncovers what the experience of the 2002 SARs epidemic reveals about this one. Both were caused by coronaviruses, but certain key changes to today's virus have allowed it to infect the world, where SARs was contained.

The third episode looks at anxiety and explores why it is so common. It talks to neuroscientists who explain the physiological and evolutionary basis of anxiety. Although it can help animals escape predators, anxiety can cause serious problems for human beings. It talks to sufferers of anxiety and examines the different types of anxiety people can feel. It also looks at how social media can cause anxiety.

A fifth of the land on our planet is covered by desert. Deserts may appear to be barren and empty, but they are of crucial importance to life. For those that can overcome their challenges they provide a vital refuge. The Grasslands are one of our planet's most productive landscapes. They support the greatest aggregations of large animals on Earth. Cameras follow desert elephants seeking sustenance, bison roaming North American grasslands and caterpillars living the good life underground.

It's Valentine's Day and Maddi steps out on her first ever date with a romantic man. Kelvin works with a relationship specialist and puts his dating skills to the test. Michael is overwhelmed when he meets the woman of his dreams.

Olivia meets someone who seems to truly get her. Andrew has found out about a speed dating event being held in town. He works on his jokes and James Bond impersonations before going to the dinner. Jimmy and Sharnae go on a special holiday together where Jimmy plans a romantic surprise.

To help Andrew in his search for love, relationship specialist Jodi Rodgers has come to work with him - on his dating skills. Olivia hasn't given up in her search for love. Today, she's on her way to meet someone new. She's meeting Jackson. Jackson likes origami and the smell of perfume. He hates the sound of nails on a blackboard and people slurping their tea. Jimmy and Sharnae are arriving at the Gold Coast for their first-ever holiday together. And Jimmy has a surprise in store for tomorrow.