Agnes was born in 1982, the inbred daughter of Billy Lenz who was raped by his mother at the age of 12. Agnes Lenz was treated like a princess by Mrs. Lenz and her lover. Little is known about those years other than this.
Those happy years however, were not to last. On the 25th of December in 1991 her brother/father Billy (who was locked in the attic by their mother) escaped the confines of the attic. Driven insane from years of abuse by Mrs. Lenz, Billy attacked Agnes when she was alone, wrapping her face with plastic, her now insane father/brother removed and ate one of her eyes. Agnes' screams in fear and pain got the attention of Mrs. Lenz and her lover, after finding Agnes on the floor bleeding and terrified, Billy brutally murdered Mrs. Lenz and her lover. After Billy is arrested by the police and sent to an insane asylum, Agnes is sent to an orphanage where she remained until 2005. Little is known about her time at the orphanage, perhaps she was taunted by her peers for her disfigured appearance, perhaps her own ghastly heritage revealed, or maybe she was abused. She spent many years at the orphanage, apparently not wanted due to be a result of inbreeding and her own deformity. At some point, she joined Billy's dark road and eventually accepted him as her "father".
In 2006 Agnes Lenz escaped the orphanage where she was housed and made her way back to her old home which was sold and turned into a sorority house when Agnes was in the orphanage. Agnes then proceeded to murder the new residents of her old home. She manages to murder a most of the sorority house's residents cutting off their heads which she uses to decorate the attic's Christmas tree. When the two surviving members Kelly Presley and Leigh confront her up in the attic she shows off her newly decorated "Christmas tree" with the bodies of all her victims underneath it. Billy, who recently escaped from the asylum, enters the house and both father and daughter close in on the survivors. However, Kelly and Leigh manage to escape from the house which has been set on fire, trapping Agnes and her father/brother in the now blazing house where it is assumed they perished in the blaze.
However Agnes and her father managed to escape the fire, following entering the hospital where Kelly and Leigh were in, Agnes appears in Leigh's room and murders her, mutilating her corpse. Agnes then attacks the last surviving member of her brother's and her killing spree, before Agnes is able to kill her, she herself is killed by Kelly who uses a defibrillator pad to electrocute her this was later followed by the death of her father/brother, ending the Lenz family line and their twisted killing spree.