SPOILER ALERT!
It's not Mark Rylance but I see the resemblance - I wondered who he reminded me of.
Right - my theory for what it's worth.
The Army Press Liaison Officer would possibly have been too young to be in Iraq? but, through his job, has knowledge of what went on there.
Stone, the butcher's wife and the one who died (Daniel's father) all did something in Iraq and he blackmailed them, found out that Stone/dead man had kidnapped Alice and Sophie and the other German girl.
He said he would rescue them but had his own agenda.
He and Alice put the body of the German girl (who may have died from malnutrition) in the shed. Her DNA (still not sure how they got much DNA but possibly the remains weren't burnt too much) matched Sam, Alice's father, because he had had a fling with a German woman and the girl (Lena?) was the result.
Lucy is the child of Alice/Sophie - still not sure which of those two she is as she spoke some French (which Alice could have learnt from Sophie anyway).
The little girl can't be Alice because Alice will be about 23 now.
Alice/Sophie has been sent to Switzerland and the nasty soldier has the child Lucy.
Sorry, I am forgetting the names! And someone else may have a different theory.