It's a fascinating concept. It was this which elevated a generic police chase story into something quite special.
In Time is set in the future, but in a world recognizable to us today. There was little going on which pointed to this advanced technology, except for what had happened to human beings.
Everyone on the planet had been genetically altered, so that they would stop aging at twenty-five years old. Great! You may say, but there's a catch.
On your 25th birthday, your personal body clock kicks into life. Displayed in digital numerals on your forearm, it counts down to the moment of your death. That time is only a year away.
Moreover, time can be transferred. With the majority of the population living in poverty, the second action of their birthday is to immediately sell most of their time. In the ghetto, people tend to live day by day, if not hour by hour.
But the ability to transfer also means that time can be given back. Factories teem with people working hard, in order to receive just a few more hours on their clock. It's generally just enough to see them through a few hours kip, then back onto the factory floor.
But one district has it all. New Greenwich is filled with the elite, who have the time capital to live forever. A millionaire has a million years banked, and so forth.
One man has already lived for over a century. He has another century on his clock. He looks twenty-five, but his mind is old and tired. He wants to end it all. So he sets out for a wild night's drinking in the ghetto, a sitting prey for marauding gangsters.
A good Samaritan emerges from the crowd and, in unwarranted repayment for his bravery, he gets the gift of his dreams. A century of life on a ghetto man's arm.
It's not something that the police-like time-keepers, nor their bosses amongst the elite, will countenance for long.