'Criminal Minds' Season 11 episode 21 watch live online: UnSub warns Dr Reid; new case related to his kidnapping in Season 2? [Spoilers]

"Criminal Minds" Season 11 is bringing an interesting case in every episode. While last week's episode 20 focused of an UnSub, who disfigured women's faces to make them look like his girlfriend who committed suicide, this week in episode 21 viewers may get transported back to Season 2.

CLICK HERE to watch "Criminal Minds" Season 11 episode 21, titled "Devil's Backbone," live. And CLICK HERE to watch the episode later online

In episode 20, we saw BAU solving the case dealing with an UnSub who, after discovering the suicide of his girlfriend, decided to perform makeovers on other women to recreate them to look like Sarah. And if his victims didn't live up to his fantasies, he would kill them the way Sarah committed suicide: by drowning.

In episode 21, we will see BAU solve the tricky murder case where two young boys are killed by an unknown UnSub, probably under the supervision of an old UnSub they had put away in the prison 15 years ago. The synopsis of "Devil's Backbone" teases that BAU reopens the investigation of the crime when the security guards at Virginia prison discovered in a package evidence linked to the incident of the missing boys with a lady prisoner Antonia Slade, played by guest actress Frances Fisher. She offers help in solving the abduction of these boys which happened several years ago. But the team believes that she might have more information about the boys and their whereabouts.

The promo of the upcoming episode shows Slade being transported and then later talking to someone from inside her cell about some missing boys. This is when Dr. Tara Lewis is seen telling the team that Slade is "orchestrating the entire thing from behind bars." The suspected UnSub is heard saying that the boys are still alive, but also warns that they won't be alive for much longer. When Hotch decides to give her what she wants, she says she wants to communicate with Dr Reid.

At the end of it, the old lady is seen grabbing Reid by the hand and telling him "there's a storm coming," before the clip closes.

Does this have to do anything with Dr Reid's kidnapping by a serial killer in Season 2 episode 15, "Revelations?"

Plot synopsis for "Devil's Backbone" (via TV Guide) reads: "The BAU enters into a dangerous game of cat-and-mouse with a convicted serial killer after guards at a Virginia prison intercept a package with evidence relating to the kidnapping of two boys several years ago. The team believes the notorious killer may have information on the boys' whereabouts."

"Criminal Minds" Season 11 episode 21, titled " Devil's Backbone," will be aired April 20 on CBS at 9 p.m.