Promises

MP Kollman's Promises is the second book in the third of the linked trilogies that make up The Brothers series and follows closely on the heels of the previous book in the series, The Accident.
In Promises, Kevin Grayson retires from the Bureau of Drug Enforcement and focuses on a new goal: repairing his relationship with Jimmy Bauer, who has been his best friend since high school.
Of course, Grayson may be retired, but he'll never stop working. He needs an outside man, just to watch his back, for a secondary goal: bringing down the main drug boss in Milwaukee, Wisconsin.
Here, Grayson's two goals collide: there's no one but Bauer he can trust to help him. Will his old friend rejoin him?