Half of England's pregnant teenagers have vanished. They didn't go missing, they just never conceived. And the teenage pregnancy rate plummeted. A real-life Whodunnit. Everyone wants to crack the case and keep rates dropping.

Michael Blastland is closing in but getting caught endlessly in an intricate spider web of causation as he tries to find the explanation for one of the most dramatic societal changes England has ever seen. He's picking off the culprits and puncturing presumptions about causation and its implications for policy making.

Encountering red-herrings, false accusations, Government conspiracy, and hack journalism, finding out whodunnit in the case of a 50% reduction in teenage pregnancy has given him sleepless nights.

At its heart may lie a Government desire to prevent under 18 conception - a well-meaning intention, backed up by some strong evidence that socio-economic disadvantage can be both a cause and a consequence of teenage motherhood. But what makes huge swathes of teenagers change their behaviour?

Whodunnit? is a new series and a new kind of investigation. It owes its style to detective storytelling. But the cases are unequivocally real. These are societal mysteries - true-life changes in the pattern of our lives, changes that might even feature some of us.

Presenter: Michael Blastland
Producer: Katherine Godfrey
A Whistledown production for BBC Radio 4. Show less