The basic premise of the movie is that the editor of a high profile french magazine had 'locked in' symdrome from a stroke, causing total paralysis with the inability to move anything but his eyes. After a three week coma, he awoke, lucid and only able to communicate through blinking.
After initially despairing, he decides to use a book contract he had had prior to his stroke to write a book on his condition, explaining that while he was trapped, he could use his imagination and memory to take him to other places. His attitude towards life and all that is within it takes a dramatic U-turn. He reconnects with his children and on the whole becomes a better human being.
The movie is visually stunning. It is all the more stunning in that it is based on a true story, and seems to be remarkably faithful to the original (ie the real world.) The camera work is probably the most innovative thing about it, and you can see why it won an academy award.