You can still listen to BBC iPlayer Radio via your browser by visiting bbc.co.uk/radio
The Time Lord is trapped underground and has to communicate with a captor that has no apparent mouth or ears.
See all episodes from Doctor Who
See all broadcasts of Episode 4 (7)
50 years of adventure! Join the Doctor for great clips, trailers, news and fun!
David Tennant, Steven Moffat, Russell T. Davies, William Hartnell, Tom Baker and more ..
Sign in to the BBC, or Register