[spoilers] Lucas. Just Lucas.

[HellsBells]

There is no doubt that series 9 does not relate to series 7 & 8. The writers clearly know less about the character than us, the viewers.
I think the fact that Beth uncovered that photo of 'real' Lucas was a big flaw in the plot. Lucas was so good at his job he would certainly have erased every trace of the real Lucas.

I think the writers wanted us to feel the same sense of betrayal that the rest of the team felt, which worked very well. But you can't do that to an established character without a really excellent story and unfortunately this wasn't it.