The "interesting story" you're referring to is likely the episode " Cradle to Grave " (Season 5, Episode 5), which is widely considered one of the series' most disturbing and memorable "unsub" (unknown subject) cases.

Subplot-wise, this episode features Chief Hotchner being unusually hard on Derek Morgan, a move later revealed to be a test to see if Morgan is ready to lead the team.

In a tense climax, JJ and Prentiss lead the charge into the Reinman home to rescue the surviving women and babies.

S5E5 - “Cradle to Grave” - Unsubs: A Criminal Minds Podcast

The couple is trying to "replace" their lost son. They keep the male babies that meet their specific criteria and discard the mothers and "imperfect" infants. Why It’s Notable

The team initially suspects a black-market adoption ring. However, the profile shifts when they realize the killers are a married couple, Robert and Linda Reinman, who lost their own baby, Michael, due to a medical tragedy.

[s5e5] Cradle To Grave -

Subplot-wise, this episode features Chief Hotchner being unusually hard on Derek Morgan, a move later revealed to be a test to see if Morgan is ready to lead the team. [S5E5] Cradle to Grave

In a tense climax, JJ and Prentiss lead the charge into the Reinman home to rescue the surviving women and babies. The "interesting story" you're referring to is likely

S5E5 - “Cradle to Grave” - Unsubs: A Criminal Minds Podcast S5E5 - “Cradle to Grave” - Unsubs: A

The couple is trying to "replace" their lost son. They keep the male babies that meet their specific criteria and discard the mothers and "imperfect" infants. Why It’s Notable