Despite a script that throws credulity out the window, the Atlantic Theater Company has given Abby Rosebrock's Blue Ridge the kind of world premiere a young playwright can only dream about. Economically directed with the steady hand of Taibi Magar (Lauren Yee's The Great Leap, also at the Atlantic) and performed by a superb cast led by the incandescent Marin Ireland, Blue Ridge centers on a group of dysfunctional misfits at a church-sponsored halfway house. Ireland's character, an AP English teacher at Blue Ridge high school whose affair with her married principal led to her taking an axe to his car, is new to the group but she wastes no time in making herself the center of attention and wrecking havoc in her new family. . . .