The series' first episode opens with a pair of schoolteachers in contemporary (1963) London, Ian Chesterton and Barbara Wright, investigating the mystery of Susan, a student who seems confused and even frustrated at how what she is learning in history and especially mathematics seems to be wrong. Following Susan to her supposed home, they discover the TARDIS in a junkyard, surprising both Susan and her grandfather the Doctor, who launches the ship in response to the discovery. Ian and Barbara are involuntarily taken on a journey back to the year 100,000 BC and spend two years adventuring through time and space with the Doctor, who at this point in the series has no control over the navigation systems of the TARDIS.