Based on the novel by Ian McEwan by the same name, the film follows Judge Fiona Maye (Thompson), as she presides over one of the most difficult cases ever presented in her courtroom: Should she rule in favour of a Jehovah's Witness family who refuses to allow their son, Adam (Fionn Whitehead), to receive a blood transfusion , despite his leukaemia diagnosis? (They argue the medical procedure would force them to abandon the principles of their faith.) Or, should she make Adam go through with the procedure that could save his life, his religion be damned? The child's fate is, quite literally, at her fingertips.