Having established Klein as a German scientist from a time line where (or when?) the Nazis won the war, this story attempts to fill in her back story. And, in particular, how she came to be in Colditz castle in 1944. This is the most interesting part of this Big Finish audio drama and involves some neat manipulations of known Doctor Who history in an alternate world. A special guest star turns up using a German version of a name that will be instantly recognisable to fans.
With my increasing enjoyment of the character arc of the questionable Klein I would have been quite happy if this section of the story had gone on longer. However it is only a prologue to the main events which feature the Doctor and Klein landing on a planet and finding themselves in the middle of a fight for survival between human colonists and the insect like Vrill. There's some clever stuff about the Vrill who use scent markers to communicate so that their messages float in the air after they have moved on. The battle for supremacy allows for some interesting discussions about Klein's political background. The Seventh Doctor is at his manipulative best and there is a great cliff-hanger ending. But all the while I was waiting to get back to Klein's story.
It is a perfectly fine Doctor Who adventure but not quite what I was waiting for. Maybe The Architects of History (which is a great title for a Who story) will complete the picture for me.
3 out of 5 misplaced Tardis keys for Survival of the Fittest but I am really enjoying this unexpected Klein trilogy. Now on to the Architects if History.