Mary Sandin is one of the main protagonists in The Purge. She is portrayed by Lena Headley
Mary is first seen preparing dinner in the kitchen, where she asks her son (Charlie) to come and help her. Her husband James returns with blue flowers for her to put outside their house to show their support. While she is outside she runs into Grace who tells her the latest neighbourhood gossip, and gives her a box of cookies. She enjoys dinner with her family and then they lockdown for the night.
She spends the night working out, reading and talking to her husband. When her son Charlie allows a stranger into the house and James kills their daughters boyfriend Henry, a group of Purgers arrive at their house, threatening to break in if they don't give him the stranger. They fail to comply because they realise he does not deserve to be killed and the purgers bring down the barricades and break in.
Mary fights off multiple purgers and her husband is killer by The Polite Stranger. While walking down one of the hallways in the house, a female purger jumps out of a corner and forces her to the ground and begins tickle torturing her. The neighbours enter their house and kill all the purgers before taking them hostage for themselves.
The stranger kills one of the neighbours and threatens to kill the others. But Mary declines his request and they spend the rest of the Purge in peace. One of the neighbours attempt to steal her gun but she attacks her with it and smashes her face into the glass. And the Purge sirens sound indicating that the Purge has concluded, she tells them to get out of her house and they leave as Charlie, Zoey and Mary stand in the doorway.