I just saw this on ET. According to Shia, Sam is coming off of heartbreak and is looking for someone to fill the void (or something along those lines), and he finds that in Carly. According to Rosie, Carly and Sam are already living together in an apartment at the beginning of the movie. Carly had been working for the British embassy, and she and Sam met in the White House. She also hinted that her boss, Dylan, could be part of a love triangle with them, and Patrick Dempsey later basically hinted that Dylan might get a little "McDreamy" with Carly.