As the mysteries of hearing are revealed, we see how technology and scientific progress are working to restore, replace, or supercharge this enormously powerful human sense. We meet a young man who shows us the potential of musical hearing and a blind man whose hearing is so acute that he can navigate a bicycle by the sound of the echo of a click. As technology starts to merge with humanity, we meet true bionic pioneers: the recipients of cochlear implants who demonstrate how the brain can learn to interpret a new synthetic sense. We discover hearing aids that surpass the ear's natural acoustic abilities and even read the brain's intentions. There are researchers working to use sound to improve cognition and memory while we sleep. And we learn how one company is developing an innovative, effective technology that uses the skin as a conduit to pass sound to the brain.