Four members of the Kingman family are found bound and murdered at a table set for six. The phonograph is playing "Jingle Bells" over and over.
While three of them have been shot to death, one - Donna Kingman - was strangled.
While the BAU crime is being debriefed via video feed from the crime site, local police tackle a blood-covered man named Ezra Warren who suddenly attempts to bolt from the house.
Warren tells Rossi that he and one of the victims - Lance Kingman - were a couple.
The team interviews Ezra Warren and Mark Clifford and discover that Frank Kingman - the family's father - was hard to get along with, always making accusations and venting his homophobia.
They also learn that Dillon was deep in debt. His father had been sending him $5,000 a month until ten months ago.
JJ interviews Dillon who tells them that Mark was the one who didn't want to have sex with Jenna before marriage. He theorizes that Mark was dating Jenna only so that he could get close to Lance. He thinks Mark is gay.
Garcia discovers that Frank has been paying a dummy company called C.L. Gilliam and Associates $20,000 twice a year for 25 years. He cut off payments ten months ago.
JJ and Rossi re-interrogate Dillon and discover that he was transporting prostitutes for a living. Prior to that his father had been paying him $5000 a month to keep him quiet about his dad's affair with a red haired woman. The money stopped when Frank told him he had broken off the affair and had come clean with his wife.
Garcia discovers the identity of Frank's mistress is Cora Gilliam, and that Frank had been paying her $20,000 twice a year.
When Reid and Rossi go to question Cora, she attempts to flee. She tells them she had the affair with Frank for 26 years, and that she had a 2-year old child when she met him. She tells them he has since graduated high school.
Reid tells JJ that the math doesn't add up. JJ wonders if the child is actually Frank's.
Reid theorizes that Cora's child had motive to kill the family. He and his mother had been dumped from the family and lost their income.
Hotch theorizes that Cora's child was actually Mark and that he is Frank's illegitimate son. He believes that Mark hadn't had sex with Jenna because she was his half-sister.
Garcia tells Morgan that Frank Clifford had grown up as Frank Powers.
Mark confronts Cora and bitterly blames her for her lies to him. He had grown up as Mark Powers because of a fictitious history, in which he was the son of Captain Frank Powers, who was lost in action while serving in Desert Storm.
He recounts the fact that every night they would set out a place setting for "Captain Powers".
He shows Cora the dead body of Frank Kingman. He makes her take a seat at the table. He tells her that he had shown up at Frank's house, and had caught him arguing with Lance. He had knocked Frank out with his gun, then forced Lance to tie everyone to their chairs by threatening Jenna with his gun. Afterward he had tied Lance up, then shot them all, except for Donna, who he strangled because he visualized her as his mother. He then re-set the table, and put on the Christmas music. He brought Frank back to his house and then killed him.
After telling her this, he prepares to kill his mother. Hotch shows up and captures him.
Meanwhile, Jessica Brooks - Hotch's sister-in-law - is babysitting Jack at Hotch's request. He later receives a call from her, asking him to pick up her father Roy from the police station. Brooks has been diagnosed with Alzheimers. Police had taken him into custody after he had broken into a store that he used to own with the intent of opening it up. The owner declined to press charges.
Jessica Brooks (Hotch's sister-in-law and Roy's daughter) tells Hotch that Roy needs round the clock care, and that she can't afford to bring someone in. She needs to put him into an assisted care facility - and idea that Roy hates.
Jessica and Hotch figure out a plan to have him move in with her. Hotch will supplement her income so she can care for him. Roy accepts.