The next episode of "Blue Bloods" will put Erin Reagan in a tough situation when her own informant goes back on her and potentially blows her case.

Episode 4 is titled "With Friends Like These" and will air on broadcast network CBS this Friday, Oct. 16 at 10 p.m., according to TV Guide.

What would an NYPD cop series be if it did not thrown in the occasional mob story? This episode will most definitely bring an old skeleton out the closet for the two decades old "frenemy" factions.

Apparently, old cases stay warm when Erin is on the case. It is her who links to a cold case that allows her to finally lock a mob boss up who has been slipping through the cracks for quite some time now. Of all things she wanted to get him on, it was an old murder she is willing to settle with that will put the episode into motion, according to Spoilers Guide.

But fans should not be naïve enough to think that she has the case in the bag just yet. It will be an old informant of hers that was in witness protection that will come out and put the whole case in jeopardy.

Vincent was the one that had helped her in the past, and she put him in witness protection to keep him alive. But he drops witness protection and comes out into the light of day to provide his old boss with an alibi for the murder, which definitely puts a new chink in his armor against the fiery Erin.

The episode will also feature Frank squaring off against the NYPD's other commissioner, Stan Rourke of the FDNY. The departmental war leads to some surprising revelations and eventually will pit the two heads of emergency crews in New York at odds against each other.

Watch a preview for the next episode below.