|A group of pre-teen girls are playing Truth or Dare, one girl is dared to, 'say Bloody Mary three times in front of a mirror'. Later the girl’s father is found dead in the house.
In the car, Sam is asleep dreaming of Jess' death. Dean wakes him, they are in Toldeo. They bribe a mortuary worker to let them see the body, whose eyes have 'practically liquefied'. At the house it is the wake, the victim’s eldest daughter, Donna, is surrounded by her friends. The younger daughter is convinced it's her fault he's dead, because she said 'Bloody Mary'. Dean assures her it's not. They snoop, discuss the legend, about a girl who appears and scratches your eyes out if you say her name three times in front of a mirror. One of Donna's friends, Charlie, wants to know what they're up to. They give a vague explanation and Sam hands her their number, just in case she sees/knows anything.
Heading to the library to research the boys find the computers are out of order. Charlie is driving, on the phone is another friend, Jill, trying to freak her out by saying Bloody Mary in front of the mirror three times. Charlie hangs up, Bloody Mary kills Jill.
Sam is once more dreaming of Jess. Dean is bored with the unsuccessful researching. Charlie, who is beginning to believe it's because of the Bloody Mary legend that Jill is dead, phones the boys who don't discourage her views. The three of them head to Jill's house where they find 'Gary Bryman' and a bloody handprint on the back of Jill's mirror.
Gary Bryman was killed in a hit and run, we learn Jill was the driver. At Donna's house the name of Donna's mother is on the back of the mirror. She died of an overdose of sleeping pills over a year ago. Dean is at his wits end, he's doing a nationwide search on Mary's who died in front of mirrors. Sam and Dean realise the criteria Mary is using is the victim must have a secret where someone died. An article is found on Mary Worthington, an unsolved murder in Fort Wayne, Indiana. Images from the scene show her dead before a mirror with the same hand-print on it.
The police officer that was on the case explains that she was found dead in front of a mirror with her eyes cut out. He believes she was trying to write out the name of her killer. Her body was cremated but the mirror still exists, which was recently sold to a company in Toledo.
Donna thinks Charlie is crazy and says Bloody Mary three times in a mirror. In class, Charlie begins to see Bloody Mary in reflective surfaces; she ends up smashing a window and running from class, she calls Sam. In their motel room they cover all the reflective surfaces. After Charlie explains what happened, the secret Mary saw, they realise that the person only needs a secret where someone died. Mary is being very indiscriminate with the killing - the secret holder doesn't even have to be the one who calls her.
At the warehouse, Sam and Dean are ready for some quality smashing, except there are a few more mirrors than they expected. When they find the mirror, Sam summons Mary to it, with his knowledge that he dreamt of Jess’ death before it happened and his belief that he could have stopped it..
Sam is being overwhelmed by Mary, Dean smashes the main mirror. This causes Mary to come through it into the world. Dean holds up a mirror and Mary scatters like glass.
They take Charlie home and drive off into the sunset.