Based on the novel by Clare Allan, Benjamin Ross's Poppy Shakespeare tells the platonic love story of two women: N, a devoted patient of a mental-health clinic in London, and Poppy, a violently unhappy new admission who's as certain of her sanity as N is of her own compromised mental state. The result is a rich, stylizedblack comedy illuminating the vast perversities of "mental illness," executed with an assured and meaningful quirkiness reminiscent of young Jane Campion. (Harvard Exit, 807 E Roy St, thestranger.com/siff. 9:30 pm, $11.)