The Voices of Silence by Bel Mooney

Flora Popescu’s parents are planning to
defect when daily life suddenly brings
frightening changes – some linked to a
friendship between Flora and a new boy
at school. Unlike his poor classmates,
Daniel dresses and eats well, and his
father ranks high in the secret police.
Flora slowly realises that her father is in
danger and only she can save him from
the secret police.