Elizabeth Masterson (REESE WITHERSPOON) is a dedicated if overworked doctor at St. Matthews Hospital in San Francisco where she's competing against Brett Rushton (BEN SHENKMAN) for a coveted attendee slot. Much to the concern of her sister Abby Brody (DINA WATERS) and best friend and coworker Fran (ROSALIND CHAO), Elizabeth is so busy she has little to no time to date and doesn't realize she's letting her life pass her by.
Thus, she's in for a surprise when she discovers that morose landscape architect David Abbott (MARK RUFFALO) has moved into her place, claiming her family sublet it to him. The two immediately clash, with her thinking he might have drinking and/or mental issues, an observation shared by his psychiatrist friend Jack Houriskey (DONAL LOGUE), especially when David claims he's the only one who can see her when she's not passing through walls, etc.
Seeking the aid of occult bookstore worker Darryl (JON HEDER), David eventually realizes Elizabeth is some sort of wayward spirit unlike his new downstairs neighbor Katrina (IVANA MILICEVIC) who's decidedly earthy in her demeanor toward him. As David and Elizabeth work through their issues and become friends and then more, they set out to discover the truth behind their situation and her otherworldly presence.