The twists and turns of an affair.
At first this will seem like a thriller of the usual mould, but not for long. Two married people begin an affair and get caught in a compromising situation by a blackmailer. The two attractive leads, Clive Owen and Jennifer Aniston, are usually interesting to watch, but it's the tight, intricate plot that is the star of this movie. The scriptwriter doesn't cheat by putting in blind alleys: everything shown adds towards the unexpected ending. It's an edgy film that makes the heart beat faster, and the plot builds into anxious tension and fear that doesn't let up, due in part to the seediness of some situations, although, as well, the director uses bright, clean, up-market surroundings to continue the sense of foreboding.
When these sorts of clever scripts work, there is something absorbing and worthwhile in watching a film that has been reasoned out without the artistic side being compromised. After "Derailed" has ended, the viewer will probably go back and put the pieces into place which had seemed something other during the viewing, and will find that everything fits.