I must say for a movie that did not have good reviews from critics, it did pretty well in the US, and is a good movie.
The story is about a woman (Julianne Moore) whos son is taken away from her, in the sense that she slowly loses her sons belongings and memories. She tries to hold onto them, but, for example, her son disappears from her photo, and everything else around her. She then approaches a man whos kid was her sons friend, but she realizes that he thinks that he had no kid! So that is the suspense of the movie, where she and the guy begin a quest for their children.
In case you do not want to read the spoilers that I am going to write here, please scroll down to Spoilers completed and read the rest!
SPOILERS START
Well, the suspense is that aliens are conducting experiements and want to see if it is possible to wipe out memories. But their experiment fails because Julianne was able to hold onto the memory and help the guy mentioned above also remember his kid. Since the experiment failed, the villian/experimenter had to return the kids.
SPOILERS COMPLETE
I enjoyed the suspense of the movie, and Julianne is a good actress. I dont know why the critics reviews were so negative. I would definitely recommend this movie.