Jimmy "The Gravedigger" Conlon (Liam Neeson) sends Michael and his family to a lakeside cabin, where he thinks they'll be safe. He goes after Sean Maguire (Ed Harris) and his gang, eventually killing them all.
In the morning, Jimmy arrives by taxi at the lakehouse, and finally gets to meet his granddaughters. They are ambushed by Price (Common), the assassin Sean Maguire had hired earlier to kill Jimmy and Michael. Jimmy is shot and mortally wounded. Michael and his family run into the woods. Just before Price can kill Michael, Jimmy pulls himself up and kills price with a rifle.
Curtis (aka "Legs), gives Detective Harding (Vincent D'Onofrio) a video recording of Maguire's son killing the Albanian drug dealers. The police now know Michael was innocent and head to the lake house where they find Michael with his dead father. In his hand, Jimmy has a last gift for Detective Harding: a list of all the people Jimmy killed over the years.
Michael returns to a normal, happy family life. He watches Legs win an amateur boxing match. As the movie ends, we see Michael now keeps a photo of Jimmy (whom he'd always hated before) in his house.
Thanks John L!