Knowing that this was about to come out, I revisited the previous two plays, Home Truths and The Drowned World, which both take the established Sara story from The Daleks' Master Plan and twist it slightly sideways. Here the story is definitely twisted backwards, and we get a lot more illumination not only into Sara's character - she must always bear the guilt of killing her own brother - but also into the motivations of Mavic Chen, the eponymous Guardian of the Solar System, and one of the most effective villains ever to appear in Doctor Who.
There's also a fantastic image of elderly prisoners forced to maintain a gigantic clock - I thought this might be based on Aldiss's Wheel of Kharnabar from Helliconia Winter, but it turns out to be inspired partly by The Hudsucker Proxy (which I haven't seen) and partly by John Noakes cleaning Big Ben on Blue Peter. (This is revealed by Guerrier in the extras track, where we also find out that Jean Marsh never actually saw her own episodes due to a) not having a television at the time and b) being very short-sighted.)
It doesn't all make perfect sense, and the three stories will probably confuse listeners who know nothing of The Daleks' Master Plan. But I enjoyed it.