The story is about a person who calls themselves "The Doctor". They travel in their space-time-ship TARDIS ("Time And Relative Dimension In Space"), with which he can go anywhere in time and space. Because of an error in its "chameleon circuit", the outside of the TARDIS always looks like a 1960s-style British police public call box (similar to a blue telephone box), but on the inside the TARDIS is much bigger.