Mercury is the subject: a liquid metal so toxic that half the material in a standard silver amalgam filling is made from it. This BBC film opens on that fact and follows the case being built against a substance sitting in millions of mouths, tracing how vapor released from old fillings gets absorbed through the lungs and oral tissue. Researchers and campaigners lay out claimed links to brain damage, kidney damage, and neurological disorders, while dentists who defend amalgam are shown removing it without precautions, a process the film says can deliver the equivalent of a decade's mercury exposure in a single drilling session. The film sets this against a dental establishment reluctant to change practice, and raises ceramic fillings as the alternative offered by dentists willing to break from standard procedure. Shot in 1994, it plays now as an early document in a fight over dental mercury that continued for decades after its broadcast, with the safety studies it questions still disputed today.