The main plot of Just Like Heaven is that a man falls in love with the spirit of a woman who still inhabits the apartment he just leased. He is very surprised to see her there. She's surprised too, because she has no idea what happened to her. The woman, played by Reese Witherspoon, is a workaholic doctor named Elizabeth who was apparently killed in a head-on collision. The man, played by Mark Ruffalo, is a depressed landscape gardener named David, who after losing his wife has taken refuge on the sofa with many a beer and little motivation to do anything else.
Elizabeth, not knowing that she is only a spirit, demands that David leave her apartment. David is freaking out because he is the only person who can see her. In an act of desperation, David has a priest perform an exorcism on the apartment. This doesn't faze Elizabeth in the slightest, just telling David that he's mopping up the holy water when the priest is done. Next, David tries Chinese mystics and the Ghostbusters, both of whom have little effect.
David finally decides to do some research of his own, which leads him to a clerk, Darryl (played by Jon Heder) in a psychic bookstore. Darryl goes to David's apartment and simply suggests that David move because he's feeling some "serious hostility" from the spirit. David says he doesn't want to move because it's a great apartment with "a view and a fireplace."
This leaves David and Elizabeth with only one other option, which is to figure out who Elizabeth is and why she is the way she is. Of course, over the course of this journey, David and Elizabeth will fall in love. Also during their journey, they meet Elizabeth's sister, her nieces, and a creepy doctor who took over her position as Chief Resident when she had her accident.
Mark Ruffalo and Reese Witherspoon make the movie work despite the fact that there are some noticeable plot holes. For instance, when they realize they can easily convince the sister, played by Dina Spybey, that David is actually in contact with Elizabeth's spirit, they decide to kill some time by moping around on a hilltop instead of telling the sister right away, buying them plenty more time.
But I digress, the film is still plenty entertaining, with good direction and some great dialogue by writers Peter Tolan and Leslie Dixon, including my personal favorite: "You have two realities to choose from. The first is that a woman has come into your life in an very unconventional way and she needs your assistance. The second is that you're a crazy person, talking to himself on a park bench."
Overall, Just Like Heaven is an entertaining and fun film that manages to transcend the few plot holes with good performances and a witty script.