Seth is an angel that appears only to those who are about to die, or are in the process of death. [He is however, visible to other angels and has conversations with them, and spends his time with one in particular, making it obvious that angels, like humans, think, speak and have opinions.] Seth, and apparently angels in general, always ask the humans what their favorite part of life was. (In the beginning of the film, a young girl looks at Seth and answers, "Pajamas.") Seth watches a heart surgeon (Maggie Rice) try vigorously to save a man's life, although the man is already dead. (He is in fact standing with Seth watching Maggie try to save him.) Seth soon becomes enthralled with Maggie, and finds that he is able to make himself visible to her. Soon their relationship turns from a mild curiosity in each other into a friendship into a quasi-love type of relationship, neither being especially forthcoming.
Later in the film, Seth meets a man in a hospital room who can remarkably tell when angels are present, much to the amazement of Seth. The man, now calling himself Nathaniel Messenger (as angels are God's messengers) eventually tells Seth that he was in fact an angel, just like Seth, but decided to become human. Seth is amazed and begins to think about undergoing this transformation himself so that he can be with Maggie (who cannot be with him because he is an angel and who is eventually asked to marry a co-worker who she has been in a mildly serious relationship with for some time). However, once Seth makes this transformation (in which he falls to Earth, which might not have anything to do with the transformation, but is symbolic nonetheless), he finds Maggie has traveled to a mountain cabin to "get away".
Seth makes the journey to see Maggie and appears cold and soaked from rain at her door step. In the cold air, she sees his breath coming from his mouth, illuminating her to the transformation he has made. Soon after, the couple have sex, Maggie telling Seth that his penis connects them and they "fit together".
The next morning, as Seth is in the shower, Maggie makes a trip to a small store some distance away (she travels on a road bicycle). On her way back, she lifts her hands off the handle bars, looks up at the sky, and enjoys the gentle ride down the hill. However, she does not realize the logging truck pulling out of a road ahead.
The next scene shows Seth running toward the scene of the accident (apparently, Seth has also acquired humanity's intuition - an unexplainable ability to "know" when loved ones are in danger or trouble), the truck driver running for help, and Maggie lying on the road, waiting.
Seth arrives at her side, and both know that this will be their last time seeing each other, though Seth refuses to speak of it. Maggie however, sees an angel by her side, although Seth, being human and not dying, sees nothing. Seth does know that they are there, telling Maggie, "Don't look at them." Maggie tells Seth that when they ask her what her favorite part was, she will say it was Seth. Maggie then dies, and Seth is left with the incredible sadness that follows the loss of someone one truly loves, an emotion that angels know not. In a mere day, Seth had become a human, experienced physical pain, physical pleasure, the joy of true love, and the devastating loss of death. Seth is next seen sitting in a living room, and all of a sudden, his former co-angel and good friend Cassiel (Andre Braugher) appears. Seth is told that this is life, he is human, and that one day, he will die as well. Cassiel then asks Seth that if he knew this was going to happen, would he still do it? Seth responds by telling him that he would rather have one instant with her, than an eternity without. The last scene sees Seth at the beach, and after looking out at the ocean, he runs and jumps in, enjoying the water and realizing that his life will go on as well, and that he'll see Maggie one day again.
