This is the poignant true story of twin sisters from China, found as babies in a cardboard box in 2003 and adopted by two separate sets of parents - one from California, the other from a remote fishing village in Norway. Neither of the adoptive parents were told their daughters were twins, but a chance sighting at the orphanage enabled them to keep in touch, until a DNA test proved their hunch had been right.
Professor Marcus du Sautoy goes in search of answers to one of science's greatest mysteries: how do we know who we are? While the thoughts that make us feel as though we know ourselves are easy to experience, they are notoriously difficult to explain. So, in order to find out where they come from, Marcus subjects himself to a series of probing experiments.