This tightly-focused episode is all about who shot and killed Teresa's driver. Both she and Wysocki assume the man behind the plot is Gibbons, so they set out to tie him to the Irish mob.
But the pair end up being mistaken, as evidence ends up pointing to the veteran officer who Teresa bumped down to janitorial service on the pilot. He had been drunkenly complaining at a bar and two of his friends took his bitching/moaning the wrong way. They actually acted upon his words regarding Colvin and arranged the hit.
Once he learns this, the cop takes matters into his own hands. He calls Wysocki to a special, veteran police-only hang out and when Jarek arrives there, he sees the man standing sitting and drinking over a dead body. He's killed the pal who shot Colvin, forcing Wysocki to arrest him.
All does not end well for Teresa, though: Antonio's mother serves her with a lawsuit because she was wearing Antonio's vest at the time of the shooting and the department won't pay his death benefits as a result. Teresa must go to Gibbons for help in that area.
The episode concludes with Wysocki in church, speaking to a nun. But it's clear Wysocki rarely attends mass. He is convinced to say a prayer, however, and cranks out a unique one: he asks God for the power/ability to find his brother's killer and shoot him dead.