‘Blue Bloods' Season 6 Episode 20 spoilers: Danny’s pursuit of a serial killer becomes personal on ‘Down the Rabbit Hole’

On Friday, “Blue Bloods” returns with a brand new episode that promises to put its audience on the edge of their seats. The highly popular series airs on April 15 with “Down the Rabbit Hole,” where Danny (Donnie Wahlberg) finds himself facing off with a familiar cunning criminal. Whilst this is not the first time that Danny encounters the serial killer, he takes the case personally this time, when the murderer deliberately taunts and mocks him. Spoilers also hint that Danny’s niece, Nicky (Sami Gayle), may also fall victim to the serial killer. Danny is hell-bent on saving Nicky and finally putting an end to the vicious murder spree.

“Boardwalk Empire” actor Louis Cancelmi returns to reprise his role as serial killer Thomas Wilder on “Blue Bloods season 6 episode 20. The upcoming installment will also feature other “Blue Bloods” cast members including Frank (Tom Selleck), Jamie (Will Estes), Erin (Bridget Moynahan), Henry (Len Cariou), Linda (Amy Carlson), Nicky (Sami Gayle), Det. Maria Baez (Marisa Ramirez) and Officer Eddie Janko (Vanessa Ray).

Spoiler alert! This update contains more "Blue Bloods" spoilers. Read on at your own risk if you have not watched the latest episode.

According to TV Guide, Danny finds a message which the serial killer left on the latest victim. It seems that the murderer is provoking him, which makes this particular investigation even more personal for Danny.

CBS has posted sneak peeks of the “Blue Bloods” April 15 episode on its official site. One preview video warns the audience to brace themselves for the final showdown between a serial killer and a cop. One scene shows Nicky in tears as she talks to Danny on the phone. “I just want my granddaughter back,” Frank says at the end of the trailer.

This is not the first face-off between Danny and Thomas. The serial killer first appeared on season 6 episode 2, titled “Absolute Power,” and again on episode 8 otherwise known as “Unsung Heroes.” In both episodes, Thomas managed to escape the authorities. This time, however, Danny is determined to do everything to end the deadly game of cat and mouse once and for all.

“Down the Rabbit Hole” is directed by David Barrett and written by Siobhan Byrne O'Connor. Spoilers Guide has named the other actors and actresses who will be seen in "Blue Bloods" Season 6 episode 20. The upcoming run will feature recurring stars Tony Terraciano (Jack Reagan), Andrew Terraciano (Sean Reagan) and Abigail Hawk (Abigail Baker), Gregory Jbara (DCPI Garrett Moore), Robert Clohessy (Lt. Gormley), as well as guest stars Steven R. Schirripa (Anthony Abetemarco), Louis Cancelmi (Thomas Wilder), Michael Beach (Agent Adam Schaeffer), Derek Klena ( Cormac Phillips), Charles Mesure (Liam Farrelly), Alex Carter (AIC Alexander Clune), Miriam A. Hyman (M.E. Emile Cooper), Hollis McCarthy (Mary Sullivan), Cullen Johnson (Farrelly's Father), Christopher M. Elassad (Uniform) and Brandhyze Stanley (Grace Michaels), Francesca Luisa Reale (Gabriella Morretti) and Stan Demidoff (John Kamping).

Find out what happens next on "Blue Bloods" Season 6, which airs in the US every Friday at 10 pm on CBS. In Australia, “Blue Bloods” airs on Thursdays, 10:30 pm on TEN.