David (Mark Ruffalo) is a recently widowed architect moving into a new apartment in San Francisco. But the apartment isn't entirely empty; it's haunted by the ghost of a woman named Elizabeth (Reese Witherspoon). And although Elizabeth can't remember much about her life, she's convinced that she isn't really dead. While David recruits Darryl (Jon Heder), an absent-minded psychic, to get to the bottom of Elizabeth's identity, he and Elizabeth begin to fall in love.