Emily Prentiss returns from Interpol, bearing doughnuts. She's filling in for Hotch, who's been tapped for special assignment by the director.
The squad takes on a new case in Florida, where a woman has been found in a barrel encased in cement. The victim was still alive when she was put in the barrel. While they're flying down, a second woman is found similarly disposed. Prentiss and Rossi debate about why the unsub is going through so much effort to dispose of the bodies.
Both victims are young, single mothers. Then another single mom goes missing. The unsub is Stuart Baker, a member of a pool-building crew, who is accelerating his kills. He performs crude chemical lobotomies on his victims before he kills them. The team figures out that Baker is trying to mute sexuality in the victims through these crude lobotomies.
Alvez and Prentiss get to know each other, taking turns psychologically analyzing each other while on stakeout at a local lover's lane, which is the unsub's dump site.. They catch two kids coming out to neck, while the hidden Baker looks on.
His routine disturbed, he runs home, freaks out and knocks out his adoptive mother Gloria with a candlestick. Baker interrogates his tied-up mother about why she adopted him. That's because he had found out that his sister Lynelle is actually his mother and he brags that he killed her because she wouldn't have sex with him. He then heaves his grandmother into a hole he had dug, mixing cement with which to bury her. He blames her for not protecting him from his lust for his hypersexualized sister. The squad gets to the Bakers' house just in time to rescue Gloria.