The appearance of Simon's new colleague, James Simon, terrifies him. Also played by Jesse Eisenberg, the new employee looks exactly like the main character but has a completely different personality. He is self-confident and charismatic, which immediately makes him everyone's favourite. And what shocks Simon the most, nobody even notices that the new employee is literally his twin. But that's entirely reasonable: for most people, it was difficult to notice "a bit of a nonperson" Simon himself. Bit by bit, James starts taking over Simon's life, and in a matter of days, gets everything that Simon has been craving for years.
Even though The Double's plot is thrilling, it doesn't lead to any explanation, so some things remain unclear. But the movie is still worth watching as it brings up relevant topics of social anxiety and identity and has a great cast. Jesse Eisenberg's acting is just brilliant. He manages to show both of his characters' personalities, so it is clear who is Simon and who is James. You can tell the difference just by watching the way Eisenberg walks, talks, and even looks at others.
Remarkably, the characters don't talk much, but all their lines are extremely valuable. Almost everything they say expresses their thoughts and shows their attitude. This leads to another feature of the film: The Double is probably the quietest movie I have ever seen. There is almost no background music, which helps to see the story from Simon's point, rather than as neutral observers. It seems like we experience the same emotions as Simon when hearing his heartbeat in the silence. We become so close to him that even comic situations don't seem to be funny anymore. We only see injustice and ignorance towards Simon and feel sorry for him.