I had to laugh listening to this - the Sontarans sound like a cross between Blackadder's hapless cronies and Dad's Army. With that, and with genuinely funny lines, this starts off as a definitely humorous story. A Sontaran crew with a hapless Major are sent behind enemy Rutan lines to the Samur - funnily enough, where the Tardis has just landed. But why is Samur not as the Doctor remembers?
I was surprised at first that the Sontarans were so far from what they always seemed to have been in the tv series - but this is explained in the course of the story; and why they are so different,and what is so special about the 7 who are sent to Samur on a `special mission' is also explained. I enjoyed the fact that these Sontarans were so distinct in their behaviours and mannerisms and had back-stories - they seemed to be more `real' than perhaps in earlier stories. But while the humour may seem gratuitous at first, it becomes part of a story that is definitely not humorous, and is tinged with horror and a little sadness.
The only grumble I have, and one of the reasons I listened to this story twice through, is that (and I'm writing somewhat cryptically here so as not to introduce a spoiler) the voice of a character in the latter part of the story is somewhat indistinct and therefore it's hard to hear exactly what is said - a little disappointing there.
The Doctor and his companions are in fine form - particularly Tegan, who hasn't learned that sometimes it's better to say nothing at all - and the interaction between them all is great. Turlough even gets to be a little more than his usual self in this story. And at the end, as the Tardis fades into the space-time continuum, Samur is changed - and the listener is left feeling a little sad about the poignancy of the story.
Fantastic story - wonderful characters, brilliantly played - highly recommended.