'Criminal Minds' season 12 return date, plot spoilers: Core character to get personal arc in upcoming episodes

Change is coming to "Criminal Minds" when CBS' hit police procedural drama returns this week. And who better to usher in said change than recurring guest star Jane Lynch reprising her role as Diana, mother to Supervisory Special Agent Dr. Reid (Matthew Gray Gubler)?
In the next episode titled "Surface Tension," Reid decides to pull his mother out of the clinical study he has previously enrolled her in to bring her back home. This happens in the midst of the Behavioral Analysis Unit (BAU) investigating the death of a homeless man. The case takes on a bizarre spin when a hieroglyph found under the armpit of the deceased harkens back to a similar hieroglyph found in past casualties.
How does this upcoming case relate to the one from a few years ago? What is the significance of the hieroglyphs, and what bizarre motivations will the BAU uncover about the victim and this particular unknown subject (unsub) that could've killed him? Is he or she really an unknown?
Also, how will having his mother home affect Reid's personal and professional life? Will Diana be able to adjust to living back with her son, or will there be unforeseen glitches along the way? Perhaps she may provide some assistance in the resolution of the week's case, especially with figuring out what the hieroglyph means.
In an interview with Entertainment Weekly, executive producer Erica Messer teased that "Criminal Minds" is about to get deeply personal with one of the show's principal characters. A revelation about this said character's personal life is set to shake up his or her professional life and take him or her on a personal journey that none of the other characters has ever been on before.
"We are not a serialized drama and yet the back nine of season 12 will be heavily serialized," Messer shared said about the upcoming arc that is expected to kick off in the next episode, in time for Lynch's return. Could this mean that the character who's about to fall on some rough times is her character's son, Reid, or is Lynch's guest appearance just one lucky coincidence?
"Criminal Minds" returns with a brand new episode on Wednesday, Feb. 1, at 9 p.m. EST on CBS.