You can read the BBC PRESS OFFICE synopsis for the Series 4, Episode 10 of DOCTOR WHO at the link supplied below. BUT, be warned, it is slightly spoilery in nature. Factually, it stars LESLEY SHARP [see above pic] playing a character called Sky Silvestry, and DAVID TROUGHTON [see pic below] as Professor Hobbes.
Also to be found in the story is LINDSEY COULSON [see below] – probably best known for playing Bianca’s mother, Carol Jackson, in the UK soap EASTENDERS. By an odd coincidence it’s directed by ALICE TROUGHTON (no relation to David though).