On 21 August 1986, hundreds of villagers in a remote part of Cameroon mysteriously died overnight, along with 3,500 livestock.

In the weeks-long investigation that followed, scientists tried to work out what had happened. How had hundreds died, but hundreds of others survived?

In 2011, scientists Peter Baxter and George Kling told Tim Mansel how they cracked the case.

(Photo: Dead cattle by the shore of Lake Nyos, Cameroon. Credit: Eric Bouvet/Gamma-Rapho/Getty Images)