Would you risk your life to save a stranger?

A local schoolgirl has been missing for weeks when Margot Lewis, agony aunt of the Dear Amy advice column, receives a letter which reads: Dear Amy, I've been kidnapped by a strange man. I don't know where I am. Please help me, Bethan Avery.

Margot knows this must be a hoax because Bethan Avery is another young girl, who went missing 20 years ago.

As more letters arrive, Margot becomes consumed by finding the sender and - unlike the police - is convinced that the disappearances of the two girls are connected.

Solving this puzzle could save someone's life - but could it also cost Margot her own?