Last week was the last episode in which Tomas Gibson appeared as the BAU (Behavioral Analysis Unit) chief Aaron “Hotch” Hotchner. This week, on CBS’ “Criminal Minds,” Interpol Agent Emily Prentiss (Paget Brewster) stopped by to help the team tackle their normal work load while Hotch was off to a temporary assignment.

After Penelope Garcia (Kirsten Vangsness), Jennifer Jareau /J.J. (A.J. Cook) and Spencer Reid (Matthew Gray Gubler) welcomed their old colleague back, Prentiss was awkwardly introduced to new member Luke Alvez (Adam Rodriguez). She profiled him after seeing his desk when he was standing right behind her. Then, “Criminal Minds” Season 12, episode 3 began working on a case.

The BAU was called to Florida to investigate the case of a woman whose body was found chopped off and drowned in concrete. The team identifies the victim as a single mother who loved her son dearly.

Before the profilers can strap on their thinking caps, another body is found of a single mother. She was also lobotomized and buried in concrete. The Unsub clearly has a problem with single mothers doting on their children.

“Criminal Minds” Season 12, episode 3 also interspersed the BAU’s investigation with the death of the Unsub’s next victim. While the team tries to nab the killer, he is busy murdering another single mother in a pool.

The third murder victim is found. The Unsub is accelerating and his cooling off period is significantly diminished. Reid notices some chemical burns on the third victim and that is when the BAU realizes that he drilled through the nasal cavities and inserted chlorine into their brains. The frontal lobe controls impulses.

We learn that the Unsub is a man named Stuart who was adopted by his mother, Gloria. Unfortunately, Gloria already had a daughter Lynelle and she suffered from a condition called Kluver Bucy Syndrome which makes its victims hypersexual.

Stuart’s sister would always sneak out of the house in provocative clothes. She slept with all of his friends. One night, he kissed her and she told him the truth: that she was his mother and Gloria was his grandmother. She refused to sleep with her son. That’s why he killed her.

Before the Unsub claimed his fourth victim – his grandmother Gloria – the BAU arrives just in time to cuff him.

The upcoming episode of “Criminal Minds” will, hopefully, give an explanation as to why Hotch left the BAU. Gibson was fired because he was allegedly involved in an on-set altercation with a writer and producer of the CBS show.

“Criminal Minds” Season 12 airs Wednesdays at 9 p.m. EDT on CBS. 

Criminal Minds Prentiss returned to the BAU to help with the workload during Hotch's absence in “Criminal Minds” Season 12, episode 3 “Taboo.” Photo: CBS