Episode 4 of in search of giants: Dr Brian Cox takes us on a journey through the history of particle physics. In this episode, we learn how Murray Gell-Mann predicted the existence of quarks. This film is part of a series originally broadcast on teachers' TV (www.teachers.tv). The series was made with the support of the science and technology facilities council (www.scitech.ac.uk). www.lhc.ac.uk, is the official UK LHC website for public and schools. Other resources can be found on www.particledetectives.net.