Dr. Emily Darrow is a pediatric oncologist and her husband, Dr. Joe Darrow, is an emergency room physician. Although Emily is expecting their first child, she decides to join a Red Cross team going to Venezuela. Torrential rains and flooding force the evacuation of the village where the team is staying. As she is about to board the bus, Emily telephones Joe to assure him she is safe. It is the last time he will speak to her. The bus plunges into a river and is swept away. All on board are drowned.
After Emily's memorial service, strange things start happening. Recalling that Emily asked him to check on her patients, Joe goes to the pediatric oncology floor. A child gives him a drawing of a wavy cross and says Emily wants him to go there. Joe is mystified and questions the child, but only succeeds in upsetting him. Other children have also drawn wavy crosses. One reports seeing Emily in a rainbow near a waterfall. At home, the Darrows' parrot Big Bird is frequently agitated and begins pulling his feathers out. Joe puts away some of Emily's belongings and the next day they are back in view. He dreams of seeing Emily at the hospital, on an elevator and at the end of a long hall.
Emily had a small birthmark on her shoulder. Because it was shaped somewhat like a dragonfly, Emily often bought items with dragonfly motifs, including a crib mobile that arrived after her death.
A young woman who unsuccessfully attempted suicide is brought in. Joe turns her over to another doctor, saying he is only interested in helping people who want to live. A nurse reports him to the hospital director, who urges Joe to take some time off but Joe refuses. He feels closer to Emily at the hospital. Eventually he is banned from visiting the children.
By now Joe's friends know something weird is going on. They invite him to dinner and introduce him to a grief therapist. She urges Joe to make an appointment but he brushes her off. He tells his neighbor and friend, Miriam Belmont, about the wavy cross and Emily wanting him to go there, wherever it is. She thinks Joe is imagining things and shares her own story about losing a loved one. Big Bird goes berserk in the kitchen and Joe calls Miriam for help because he has to go to work. When he returns, she shows him a wavy cross drawn in a pile of dirt from a broken flowerpot. The cross is also drawn on the windows. Miriam thinks Joe did it himself and begs him to get help.
Joe visits a nun, Sister Madeline, who was fired from the hospital because she overstepped her bounds by interviewing children about their near-death experiences. At first she won't talk to him but once convinced he is not a reporter, shares what she believes. This convinces Joe more than ever that Emily is trying to contact him. He even speculates that she might not have died after all.
Joe's behavior continues to raise concern at the hospital. Everyone thinks he is on the verge of cracking up. One night he is asked to stay with a patient until the kidney transplant team arrives. The man is dead but his heart is kept beating by machines. Suddenly the man calls Joe's name, twice. When the team arrives, Joe refuses to let them touch the man. He gets into a fight and is arrested.
Miriam, who is an attorney, picks him up at the police station. She has talked with the hospital director and they aren't pressing charges on the condition that Joe take an extended leave of absence. He accepts his friends' invitation to go on a rafting trip and puts his house up for sale. While studying a map, he finds the wavy cross. It symbolizes a waterfall. On a map of Venezuela, Joe finds a waterfall near the village where Emily was staying. He takes the next flight to Venezuela.
When he arrives, he is met by a guide. The village where Joe wants to go is nearly inaccessible since the flood. In any case the guide tells Joe he cannot go there without permission. Joe insists on going and they get as far as the river. The floodwaters have receded enough so that Emily's bus is visible. The guide tells Joe they must go back. But he jumps into the river and manages to reach the bus. He forces the door open but the bus is empty. His added weight causes the vehicle to drift and submerge. On the verge of drowning, Joe sees Emily. She pulls him to safety and he collapses on the riverbank.
When he catches his breath, the guide is waiting to take him back. But Joe runs toward the village, believing that against all odds Emily survived. The natives are suspicious and threaten him with their spears. He holds up a picture of Emily and they recognize her. The guide translates that Emily came to them via the river, dying. They could not save her body but they saved her soul. A woman leads Joe into a grass hut where a baby girl is lying in a basket. At last Joe realizes what Emily was trying to tell him; that their baby survived. He picks the baby up and sees a birthmark on her foot. The native woman repeats a word that the guide translates as "dragonfly."
He wraps the baby in his shirt and leaves. In a voice-over, he doesn't know if Emily was in her right mind enough to see the baby, nor how the child survived a premature birth in the jungle. But Emily wouldn't give up until the child was safe in his arms.
Several years later, Joe and his daughter are shown playing outside on a beautiful autumn day. The little girl has Emily's curly blonde hair.