A deeper look at the global network of commerce that comes with the flavouring of our food. Marnie Chesterton visits the UK's Kew Gardens, and gets a better understanding of the horticulture behind many of the world’s most popular spice plants. Simon Jack tries to understand the appeal of competitive eating when it comes to heat, sampling some hot sauce made with the Naga Viper chilli. Plus, we hear about the business behind growing the world’s hottest chilli pepper. And, Polly Russell of The British Library reads through one of the oldest recipe scrolls in modern English to show us how spices were used in the courts of kings.