When her teenage son Robbie's drink is spiked, Olivia Somers is devastated. She has spent her adult life trying to protect people and keep them safe - not only as a mother, but also in her chosen profession as a doctor.
So she tries to put it down to a horrible accident, in spite of the evidence suggesting malicious intent, and simply hopes no-one tries to endanger those she loves again.
But someone from the past is after revenge.
Someone closer to her family than she could possibly realise.
Someone who will stop at nothing until they get the vengeance they crave.
And, as she and her family come under increasing threat, the oath that Olivia took when she first became a doctor - to do no harm to others - will be tested to its very limits.