The Invention of Lying takes place in a world not unlike our own. Except for one huge difference: People cannot lie. They are blunt and truthful all the time, which is not fun at all.
Then one person discovers that he can tell lies. He, of course, proceeds to take advantage of this ability which no one suspects.
The movie was funny. However, the main romantic plot was a bit underwhelming. The most fun was observing what little differences the writers have put in the movie’s world where no one can tell lies as compared to real life.
I would rate the movie 8/10.