Martha Jones is introduced in the 2007 series of "Doctor Who", first appearing in the episode "Smith and Jones". When the hospital she works at is moved to the Moon, Martha helps save the day alongside an alien time traveller known only as the Doctor (David Tennant). To thank her for her help, the Doctor invites her to join him for one trip in his time machine the TARDIS, but he later accepts her as his full-time "companion", admitting that she was "never just a passenger", and he even gives her the key to the TARDIS. Nevertheless, she becomes frustrated because the Doctor does not realise her feelings for him, When the Doctor falls in love(while believing himself to be a human) in the "Human Nature"/"The Family of Blood" two-parter, a pained Martha claims "You had to go and fall in love with a human... and it wasn't me". In the last episode of the series she spends a year travelling the world in a plan which saves the Doctor and reverses time, undoing the Master's actions.