Whilst the Earth and Venus are similar sized planets, often leading to them being called 'Sister Planets', both appear to have very different atmospheres, and potential living conditions. But this has not stopped scientists throughout the ages believing that there may have been life on Venus at some point in the distant past, but that something happened to send that planet into a different direction to ours. This film sets out some of the theories relating to the life-supporting potential of Venus, and compares our planet with it.