he third series of British science fiction series Doctor Who was preceded by the 2006 Christmas special "The Runaway Bride". Following the special, a regular series of thirteen episodes was broadcast, starting with "Smith and Jones" on 31 March 2007. In addition, a 13-part animated serial was produced and broadcast as part of Totally Doctor Who.
The series stars David Tennant as the tenth incarnation of the Doctor, an alien Time Lord who travels through time and space in his TARDIS, which appears to be a British police box on the outside. In the Christmas special he is joined by Catherine Tate as Donna Noble. The series also introduces Freema Agyeman as the Doctor's new companion Martha Jones, who leaves at the end of the series due to her unrequited love for him. John Barrowman also reprises his role as Captain Jack Harkness in the final three episodes which serve as the finale. The series is connected by a loose story arc consisting of the recurring phrase "Mr Saxon", which ultimately is revealed to be the return of the Doctor's enemy Time Lord the Master, first played by Derek Jacobi before regenerating into John Simm.Overview from themoviedb.org