For an audio story, this does something rare: it uses sound to its advantage as part of the plot. This story revolves around a sound wave alien, so sometimes you're unsure if the voice you've just heard is the person you thought it was, and it leads to some wonderfully chilling and eerily unnerving moments, helped enormously by the actor playing the sound wave. This story could not be told on television; trying to do it in a visual medium would be a pale echo of what you get here.

Unfortunately, the identity of the sound creature is so obviously signposted from Part One that it makes the reveal at the cliffhanger to Part Two utterly ineffective.

Aside from that, however, I really can't find anything to dislike about this story. Colin Baker gives us the Sixth Doctor as he should have been, and Peri in this one is a little laid back but perfect nonetheless. The sparing use of background noise and incidental music is a pretty brave move, but it enhances the atmosphere so much as every voice and noise you hear ultimately draws your attention.