Marin Ireland (Ironbound, reasons to be pretty), one of our most talented stage actors, seems incapable of giving a less than compelling performance. In this dark drama by Martin Zimmerman now at Roundabout Underground’s Black Box Theatre, she plays a professor in a “concealed carry” state, who is morbidly afraid that some male student, unhappy with a grade, might settle his grievance with a gun. As a single mother, her main fear is that no one would be there to raise her only child. When a gunman does strike, it is not at the university, but at her son’s elementary school. Her son is one of the victims. She deals with her grief in quite unexpected ways. While the acting is impeccable, the material seemed a bit formulaic. During the last 15 minutes, the play took what I felt was a wrong turn that undermined some of its force. The set design by Rachel Hauck is minimal in the extreme — a platform with a black wall behind it. Emily Rehbolz’s costume does not call attention to itself. The lighting by Jen Schriever very effectively enhances the production. Leigh Silverman’s (Violet, Chinglish) unfussy direction is assured. It’s only an hour long, but it’s a very intense hour.