The 07.44 am train from Brighton to London: The carriages are packed with commuters. One woman occupies her time observing the people around her. Opposite, a girl applies her make-up. Across the aisle, a husband strokes his wife's hand. Further along, a woman flicks through a glossy magazine. Then, abruptly, everything changes: A man collapses, the train is stopped, an ambulance called. And for three passengers that particular morning, life will never be the same again.