Recap: Will Frank Be Told, "You're Fired"? Two Politicians Threaten The Commissioner's Job On "Blue Bloods"

[Spoiler alert!  The following contains spoilers from "Blue Bloods"]

Police Commissioner Frank Reagan (Tom Selleck) found himself being threatened with dismissal while his detective son Danny (Donnie Wahlberg) battled a serial killer on Friday's episode of "Blue Bloods."

For Frank, it's all about job insecurity when he gets caught in the middle of a political rivalry.

New York City Mayoral candidate Katherine Tucker (Mary Stuart Masterson) confronts Frank at a dinner honoring police officers to ask about a secret investigation of her husband.

Although the commissioner knows nothing about the case, Tucker threatens that when she becomes New York's first female mayor, "You can kiss this job goodbye."

Later, Frank's aides inform him that the current NYC Mayor, Carter Poole (David Ramsey) had launched the investigation into Tucker's husband for corruption but nothing illegal was discovered.  However, investigators did find that the man had an affair with another woman.

In a meeting with Mayor Poole, Frank asks why he'd authorized the probe -- while Poole threatens the Commissioner's job and demands to see the file on his opponent Tucker's husband.

But Frank refuses to give Poole the information as the man hadn't broken any laws.

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The Mayor says they should be on the same side and warns Frank, "Don't make me replace you."

During the episode, both Frank's father Henry (Len Cariou) and his aide Garrett (Gregory Jbara) advise Frank to comply with the mayor.

"You're alienating the incumbent and his potential successor," Garrett points out.

And former police commissioner Henry believes Frank might wreck his daughter Erin's (Bridget Moynahan) chances of becoming a judge—as Poole is considering helping her make it to the bench.

But Frank says he can't let that influence him, and instead holds a pow wow with Tucker in which he tells the mayoral candidate that her husband's business came up clean—but he had cheated on her.

Frank won't confirm to her that Poole was behind the probe, but lets her know he has sized her up, concluding, "You already knew about your husband's affair."

With viewers guessing it's not the last we will see of Tucker, Frank calls her a controlling person – but insists he means it as a compliment as the two share a wary truce.

There's just as much drama for his son Danny as he and his partner Maria Baez (Marisa Ramirez) investigate a sick serial killer who has dumped three female bodies in the woods.

Danny tells a reporter at the scene that the killer is a coward.

A forensics expert informs Danny the murderer strangled the women after bludgeoning them—and then had sex with their corpses.

Later, a fourth body is found—with a note attached to Danny, taunting him, "Now let's see who's the smart one."

Danny is sorry for speaking to the reporter because it looks as though it's emboldened the murderer to strike again.

Later, the killer calls Danny and says, "You called me a coward on television. That's not true."

He puts Ashley, the latest woman he's kidnapped, on the phone to Danny to beg, "Please don’t let him kill me."

Discovering that the victims seem to have been looking for places to live, Danny asks Maria to find real estate agents accused of sexual assault, and she pops a name and address for Thomas Wagner.

Danny breaks into Wagner's home to find bloody Ashley tied up—and is just able to call for police backup when the creep sneaks up behind him and incites a bloody fight.

Cops arrive but the suspect has run away and Danny lands in the hospital with two broken ribs and 28 stitches, upsetting his wife Linda (Amy Carlson).

Although Ashley is alive and reunited with her mother, the killer is on the loose and makes time to phone Danny and sneer, "I win."

Although the detective vows he will find him, as the episode ends, viewers see the killer ogling a group of girls.

Also on Friday's "Blue Bloods," Officer Eddie's (Vanessa Ray) father, a convicted swindler, is in the hospital after being assaulted in the prison laundry room.

Eddie believes her dad might have been dealing drugs, but it turns out he got beat up for being a whistleblower.

Her father explains he stole in order to give her a better life and Eddie hugs him in a moment of reconciliation —but then he must go back to prison.

During the show's Sunday dinner scene, Frank asks Erin about her interview to be a judge and his daughter believes she is being closely scrutinized because she's a Reagan.

Frank suggests that she could run for the judgeship in the next election instead of being appointed, but Erin says that could be a much harder road.

"Blue Bloods" airs Friday on CBS.