Her whole world hinged on the moment one man jumped. On a perfect summer's day in Paris, tourists on a river trip watch in horror as drama unfolds. A small boy has fallen overboard and disappeared below the surface of the water. As his mother stands frozen to the spot, another passenger jumps. This is the story of how a single act of courage transforms the lives of all those involved: the hero James and his wife Alexa; Holly, the young mother of the victim; and Holly's mother Joanna, whose whole adult life has been lived in the hope that her daughter will never make the same mistakes she did.