A test oF whether a play has entered the repertoire is a successful revival 15-20 years after its premiere; and the examination is especially severe if the initial impact involved shock value. Bryony Lavery’s Frozen, first seen in Birmingham in 1998 in a production that had high-profile transfers to the National Theatre and then Broadway, now comes to the Park Theatre, in a version by the Blueprint Theatre Company, an outfit that specialises in revisiting plays from recent history.Frozen alternates monologues from four participants in a tragedy with dialogues between them. A Brummie mother called Nancy, broken but refusing to go under, is first searching for and then mourning her daughter, Rhona – a character never seen and yet dominating the play – who went missing at t