TARDIS stands for Time And Relative Dimension In Space and looks just like a wooden Police phone box from the 1950s on the outside, but is of infinite proportions on the inside. This incredible time machine is piloted by the Doctor, a mysterious Time Lord, and is able to transport him anywhere through time and space, disappearing in one place and reappearing somewhere new.
Of all the people who have travelled with the Doctor, River Song is the most enigmatic of them all. She always seems to be one step ahead of the Doctor, even when he’s in her past. Nobody has been able to figure out how River knows the Doctor so well, although there have been plenty of guesses! River carries a small blue book with her, wherever she goes, which seems to be a diary of her past, and the Doctor’s future. Whatever is written within, River will only say one word about her book-- “Spoilers!”