Martha Jones held possession of a TARDIS key.
History[[edit] | [edit source]]
The Tenth Doctor gave it to her after she became a regular companion of his. (TV: 42)
By welding her key to the Archangel Network, the Doctor enabled Martha to go unnoticed via a perception filter as long as she wore the key around her neck. (TV: The Sound of Drums) This ability allowed her to elude the Toclafane during the Year That Never Was. Ultimately, Martha took off her key when she surrendered to the Saxon Master. (TV: Last of the Time Lords)