I love the twist of Elena spying on her husband on behalf of Harry. I just hope that Sacha is not Harry's son. I love even more the twist of somebody impersonating Harry. I bet that Ruth will find out who and why somebody is pretending to be Harry. Could it be Mace or Juliet behind this treachery?

I was thinking the same thing and hoping that wont happen! Its a huge fear that Sasha could end up being Harry's son as a result of Elena being Harry's asset in Berlin in the 80's... anything could have happened during the time they were working together.
And its great twist to have someone pretending to be Harry, it's going to make life very difficult for him, and makes it very easy for someone to set him up and have the evidence to back it up, that could also make it very hard for Ruth to believe him if he does get set up at some time in S10...(Its a little like the situation in 9.6 where Harry's being voice impersonated... how can you disprove something if it came from the person themselves, at at least what appears to be that person?)
And could that be the return of an old face? An old Spooks character returning turned Traitor trying to get back at Harry? I dont think its Juliet somehow, but Mace...I could see it being him. Definatly not Tom since he and Harry were on good terms when Tom was decommissioned could it be Tessa? or could the returning character be Malcolm who simply is there to help Harry out of a tough spot?

Could it be the HS who somehow survived Harry's whisky? That would be truly awful. I do not know how Harry could extricate himself out of that one. Ruth would not be too surprised as she suspected Harry to be behind the HS's death. However, the more I think about it, the more I believe it is Mace who is the culprit. According to previous press releases, both Harry and Ruth were threatened to be destroyed.

And also those around Harry might be destroyed.... but it always mentions Ruth in particular. Mace knows Harry and Ruth are close, and since he nearly destroyed them both in 5.5 because of their relationship I think it could be Mace, he seems the most likely. Dont think its the HS, Ruth had the autosy results for him so I guess he's dead and gone.
Its going to prove interesting how Harry deals with it all in S10, Ruth might be the only person he can go to for help if he's in trouble, but this secret is so bad, she doesn't trust him, its going to be a tough season for poor Harry

there is a flag of the Soviet Union (hammer, sickle) during the Cold War next to Harry and a British flag next to Ruth. What is the meaming of these 2 flags? I do not believe that it implies that Harry is loyal to Russia, rather that he might have had a liaison with several Russian agents (remember Maria (?) in 7.7; Elena) or even a son with Elena. Or is it just an interpretation of S10 by Prime Focus Drama?

I am really looking for to S10 interaction between Peter Firth and Johnathan Hyde. I saw Johnathan last month in Rattigan's Nijinsky and he is a superb actor. Very physical and an amazingly expressive face.