In Quest for a Cure, Peter Day reports on whether the US Food and Drug Administration will licence the HIV/AIDS drug Maraviroc.
Maraviroc, a new HIV/AIDS drug was developed by Pfizer - the world's largest pharmaceutical company - at its vast research and development centre located at Sandwich in Kent, on the southeastern tip of England.
In the first two episodes (broadcast last year), the series examined how the drug was discovered - by screening millions of compounds in search of just one with the right efficacy and tested at vast cost, on thousands of volunteers.
In the final episode, the story reaches a climax with the public hearing into maraviroc organised by the US Food and Drug Administration in Washington DC in April this year.
At this extraordinary event, a panel of independent experts hear evidence for and against the drug in question. At the end of the day the panel vote, in public. For the Pfizer scientists it was the climax of years and years of work, involving thousands of people and millions of dollars.
When the result was announced - a unanimous yes vote - the team watching on CCTV back in Sandwich cheered and clapped ; some even shed a tear or two. As one researcher remarked "this doesn't happen very often..."
The next step should have been a formality, with the expectation that the FDA would ratify the panel's recommendation a few weeks later, but - surprisingly - it did not.
To find out what happened next, listen to Quest for a Cure with Peter Day on the BBC World Service.