Smell is the most mysterious and romantic of the five senses. It is also the least understood. This lack of understanding derives partially from the fact that smell cannot easily be described. However, it is known that smell conveys the strongest and most long-lasting of our memories. It takes only the faintest scent to remind us of the time when we first smelled it and bring emotions connected with it rushing back. This Horizon program tells the story of the race to be the first scientist to unravel the sense of smell, and of biophysicist Luca Turin and his radical theory.