Marth Jones (played by Freema Agyeman) didn't follow the Doctor at the end of the current series of Dr Who, but she is not going to be out of the Doctor Who world.

Martha Jones will come back in Torchwood.

Show producer Russel T Davies said "Now we are taking the character of Martha into brand new territory with a starring role in Torchwood."

Then she will pick up the pieces with the Doctor in the second half of the fourth series.