Agyeman appears in the role again for the final two episodes of the series , `` The Stolen Earth '' \ / `` Journey 's End '' , where she has been promoted to a US division of UNIT and is working on a top secret teleportation project based on Sontaran technology .
She first appeared in the episode `` Reset '' as part of a three-episode story , Later in the Fourth Series of Doctor Who , Martha returns for a three-episode arc beginning with `` The Sontaran Stratagem '' and ending with `` The Doctor 's Daughter '' , Agyeman appears in the role again for the final two episodes of the series , `` The Stolen Earth '' \ / `` Journey 's End '' , where she has been promoted to a US division of UNIT .