The whole population aged 22 or over, receive one morning a box holding a string representing the length of the live of the recipient. The book follows a few people:
Maura, a short-stringer, is in a relationship with Nina, a long-stringer. She goes to a support group a meet Ben and Hank. Amy, the sister of Nina, doesn't open her box and after a lot of doubts, accepts to date Ben, a short-stringer, with which she will have two kids.
A second group, made of the Hunter family show the political side of the story: one president elect, his wife, a nephew and his friend.
When the population discover the boxes and its meaning, people react a bit crazy: short-stringer freaks out and being based in the US end up shooting other people, while long-stringer feeling invulnerable try crazy stupid dangerous stuff. This will induce a discrimination against short-stringers until enough momentum is gathered to get their existence recognized as valuable as any other one.
The story is mostly based in New York and feels indeed very american: extrem reaction on the box discovery, political separation of the population in two groups (short-stringers supporters vs people afraid of short-stringers). That's the aspect that I liked the less in the book.
Otherwise it's quite easy to read.