A naked woman in red high-heeled shoes is poised on the edge of Clifton Suspension Bridge with her back pressed to the safety fence, weeping into a mobile phone. Clinical psychologist Joseph O'Loughlin is only feet away, trying desperately to talk her down. She whispers, 'You don't understand', and jumps.

Later, Joe has a visitor - the woman's teenage daughter, a runaway from boarding school. She refuses to believe that her mother would have jumped off the bridge: she wouldn't have committed suicide and she was terrified of heights.

Joe wants to believe her, but how could a woman be driven to such a desperate act? And who might drive her to it?