Jim Al-Khalili investigates the amazing science of gravity, recreating groundbreaking experiments, including the moment when Galileo first worked out how to measure it. He investigates gravity waves, finds out from astronauts what its like to live without gravity, sets out to find where in Britain gravity is weakest and so where we weigh the least, and helps design a smartphone app that volunteers use to demonstrate how gravity affects time and makes us age at slightly different rates.