Brotherhood: Though other series on the Showtime schedule may get more attention -- Weeds, we're talkin' about you -- Brotherhood just may be the best. Beginning its second season tonight, the story -- about the Irish Caffee brothers and their best friend on opposite sides of the law in the ethnic stew pot of Providence, R.I. -- makes for compellingly brutal drama. As last season ended, the marriage of Sen. Tommy Caffee (Jason Clarke) and wife Eileen (Annabeth Gish) was going down in the flames of infidelity; low-level mobster Michael Caffee (Jason Isaacs) suffered a major beat-down; and cop Declan Giggs (Ethan Embry) was tumbling headlong into despair as his friendships and relationships frayed. As for season two: Let's just say it looks like happy endings will be few and far between. 9 p.m., Showtime