I find it odd, in a way, that the Marshal (under instructions, of course) goes through so much trouble to destroy K-9, then is overtly friendly and accommodating towards The Doctor in the hopes that he can help Atrios. Surely the Marshal would know that The Doctor might not only need K-9 to help him, but that The Doctor would most assuredly be upset when he found out that the Marshal was the one who destroyed the machine?
The clues towards Astra's eventual fate are laid out fairly early here - a little too early, in my opinion. Early in Episode Two, The Doctor almost reveals that he knows what the sixth segment is well before the story is ready to reveal the surprise. Now we all know what to expect, and we're left with what we think is the main thrust of the plot (the Atrios-Zeos war) to keep our attention until the big payoff at the end of the story. At least there's some great banter between The Doctor and the Marshal to help pass the time.
And what Astra sees in Merak is beyond me. Never before has there been a more limp patsy of a man, wandering about corridors shouting plaintively for Astra. Every scene that Romana has to cut him off or shush him, I keep hoping that she'll just clock him one and end all of our miseries.