Based on the infamous true story from the late 1970s to early 1980s, Johnny Depp stars as James "Whitey" Bulger, a ruthless Irish-American crime boss who climbed the ladder to the top in south Boston as the leader of the Winter Hill Gang.  In some part, it helps that his brother Billy is a highly influential politician in the area, but his biggest breakthrough on the fast-track to success comes when a childhood friend named John Connolly happens to be an FBI Agent assigned to take down crime bosses in Boston, and uses Bulger as an informant to take down what was then bigger fish in the city.  Bulger is no rat, so he says, but if there's a way to take down his competition while also affording his own activities some protection, he's also no fool either.  He takes the offer to exchange information for the authorities looking the other way, and soon both Bulger and Connolly gain instant success and influence in their respective positions, though things get more complicated when the murderous, drug-selling, arms-dealing, extorting, racketeering Bulger's protection allows him to become the biggest fish in the pond.