Danny took things personal in "Blue Bloods" season 6 episode 20 while Erin and Anthony are set to look for a witness in a trial in episode 21.

"Blue Bloods" season 6 episode 20 is entitled "Down the Rabbit Hole." According to Spoilers Guide, Danny viewed serial killer Thomas Wilder's message in the episode. As per the publication, Wilder included a message to his most recent victim, which taunted Danny and personalized their chasing issues.

According to Christian Post, Wilder's move is something that ignited Danny and prompted him to take his job at a more personal level and boost his crusade against the serial killer. While it is revealed that Danny viewed it personally, its effect on the other aspects of his life, as well as to other people around him are yet to be revealed in the succeeding episodes.

Wilder appeared in "Blue Bloods" season 6 episode 8, entitled "Unsung Heroes." As per the publication, the episode saw the NYPD go to high alert, after the series of murders reportedly committed by the psychotic killer. His deeds did not only involve people unrelated to Danny, but also the latter's family and his special woman.

In fact, Danny's niece Nicky was also involved in the clash, as she was reportedly abducted as a hostage. Thus, Danny's family is assumed to make their move to protect their family members.

It is also assumed that the war dynamics between Wilder and Danny intensified in "Blue Bloods" season 6 episode 20, since Wilder said in the promo trailer that he and Danny would be inextricably linked together. "A serial killer and a cop," the murderer said.

In "Blue Bloods" season 6 episode 21, entitled "The Extra Mile," Erin and Anthony will look for a key eyewitness, who left a trial due to fear of being killed by vengeance. The two are set to search for him and persuade him to testify. Also, Garrett attempts to convince Frank to attend the Police Union party in the episode.

"Blue Bloods" season 6 episode 20, "Down the Rabbit Hole," aired on April 15 while episode 21, "The Extra Mile," airs on April 29.