When you step into the cell theatre you are instantly transported to a 12-year-old girl's bedroom in an affluent Florida suburb. Blue ribbons for equestrianism mingle among pillows embroidered with inspirational quotes. Horse photos accented by glittery puff paint decorate a small vanity. This is the lair of Ashleigh (Olivia Macklin), president of the Lady Jean Ladies, a club for adolescent horse enthusiasts. Jenny Rachel Weiner's Horse Girls (now making its New York debut in earnest after a workshop at last year's ANTFest) gives us a hilarious and terrifying peek inside one of these secret meetings. Be warned: This is not the special episode of My Little Pony: Friendship Is Magic that its outward appearance might suggest. In Weiner's world, friendship may be magic, but it's the kind one used to reanimate the dead and summon Lucifer. Beneath this play's pink-and-white veneer bubbles a dark sensibility that, in its examination of adolescent gal pals, is far more Heathers than Mean Girls. If Ashleigh is the queen bee, Tiffany (Angeliea Stark) is second in command and the one serious threat to Ashleigh's primacy. She's the only other girl who owns her horse; the rest ride on a whole stable owned by Ashleigh's family. These equestrian hangers-on include Tiffany's younger sister Robin (Maddie Sykes) and Margaret (Kaley Ronayne), the brace-faced misfit Ashleigh suspects is a lesbian. There's also early-bloomer Camille (Anna Baryshnikov), who has brought along her visiting Manhattanite cousin Trish (Eleanor Condo), much to Ashleigh's chagrin. As president, Ashleigh is all about harsh enforcement of the rules.