Release Message:  With Tegan (Janet Fielding) and Richard under alien control, the Doctor must get to London before the Terileptils release their improved strain of black death upon the world.

Description:  With Tegan and Richard under alien control, and the manor sealed against anyone leaving or entering, it's a question whether or not the Doctor can get to London before the Terileptils release their improved strain of black death upon the world.