the return of an old face

[loladom]

Given that Harry is facing an inquiry (that we know from S9) and the press announcements about Harry's secret hidden in his past, it needs to be someone who knows things about him. In my opinion, that rules out Tom and Zoe. They're not far enough/deep enough from his past.

SO I'll go for :

Series 10 Spoiler: show

Mace getting out of prison seeking revenge - he knew H from way back.
Tessa - who seemed to know more about N.Ireland etc. and all they knew of each other back in the day
or Juliet - she met H in Europe around the time of Omega and she disappeared after Yalta exploded
All 3 would have an axe to grind with Harry and would know far far more than Tom or certainly Zoe ever could.

Furthermore, Keeley and Peter were overheard in late January talking about how they could get Zoe back in. I'm assuming the script outlines and casting decisions would've been decided by then given they slow contracting pace of the BBC and shooting beginning in March?