NOTE: This is a first time spoiler sent in by Kate.

A flashback shows Sydney Wells (Jessica Alba) and her older sister playing with firecrackers as young children.  A firecracker accidentally goes off very near Sydney’s face, blinding the young girl at age 5.

20 years later, Sydney is an accomplished classical violinist whose blindness has only enhanced her other senses.  Under the advice of her sister – who still feels guilty that she was unharmed in the accident long ago – Sydney undergoes a full corneal transplant and regains her sight for the first time.  Sydney must spend some time in the hospital so her eyes and mind can get used to the fact that she has her sight.  While she is in the hospital, she befriends her roommate, only to have the roommate die soon after.  Confused and disoriented while adjusting to her sight, Sydney sees the very-much-able-to-walk roommate being led away by an unrecognizable figure after the doctors declare her to be dead.  Later in the movie, Sydney will realize that this figure was perhaps an angel leading the roommate to heaven – or something more sinister.

Sydney enlists the help of a therapist, Dr. Paul Faulkner, to help her adjust to her sight.  She hesitantly explains her vision to Dr. Faulkner, who writes the vision off as a trick of the mind.  He explains that the mind needs to get used to the idea of sight just as the body does, and it may take awhile.  However, Sydney’s visions only grow stronger.  In particular, she sees visions of fire, of death and, most importantly, the number 106.  She also sees visions similar to that of her roommate at the hospital.  One eerie image takes place on a public street, as a woman walks right through Sydney, before Sydney turns around and realizes the same woman is dying of a heart attack on the street behind her.

The last straw is when Sydney enters a Chinese restaurant, only to have the restaurant explode in flames around her.  She suddenly realizes that she is standing in a long-since-burned-down building, and knows now that her vision this time was of the past and what happened to that building.  Very scared, and now wishing she had left well enough alone and remained blind, Sydney runs back to her apartment and smashes all the lights, drapes curtains over the windows and lays in her bed with her eyes covered.  She does not leave this tomb until her therapist forces his way in and demands her to do so.

Convinced these visions have something to do with her corneal donor, Sydney convinces Dr. Faulkner to drive her to Mexico so she can meet with the family of the donor, Ana Cristina Martinez.  The two find Ana’s mother, who, it appears, is about to tell them something important when Sydney has a vision similar to the vision of the woman on the street – and Ana’s mother dies of a heart attack right in front of them.  Dr. Faulkner accompanies the woman to the hospital as a formality, but Sydney stays behind and explores Ana’s room.  New visions of Ana’s past, coupled with discoveries in her room, finally explain all to Sydney. 

Ana considered herself responsible for a factory fire that killed many of her co-workers and severely disfigured her own mother.  After the fire – which was an accident - she spent much of her time crying in her room and refused to go out in public, which only convinced the deeply superstitious neighbors of her fault in the fire.  The neighbors began to call her a witch and mercilessly bullied her, until Ana was driven to hang herself.

Satisfied with her discovery, Sydney meets up with Paul and the two begin the drive back to the U.S.  However, upon reaching the border, they discover the border is closed due to the threat of a high-speed chase involving dangerous criminals taking place on the U.S. side of the border.  Suddenly, Sydney is overwhelmed by her visions that have taken place throughout the movie, such as the number 106, fire and, of course, death.  She suddenly notices that a large gas tanker sitting directly in the middle of the waiting cars is labeled with a large “106.”  Also in the group is a camper with young children, and many other cars stuck in the traffic jam.  Sydney realizes that her visions were not, in fact, of the past, but of the future.  She leaps out of the car and begins screaming at everyone to get out of their respective cars and clear the highway.  Although they think her to be crazy, they do so, and just in time – one of the cars involved in the chase smashes through the closed border fence and into the tanker, causing the tanker to explode and systematically light every car waiting there on fire.  If it wasn’t for Sydney, nearly every passenger in every car would have died a fiery death.

The movie closes on a scene of Sydney playing her violin to a packed concert hall.  It turns out she was again blinded in the accident by shards of flying glass, but we can see she is happy and content this way.