Bug is William Friedkin’s best film in at least two decades, a compliment that must be tempered by the disclaimer that, after its first thirty minutes, this adaptation of Tracy Letts’ stage play (written by Letts) begins to lose its sure-footing. Those first thirty minutes, though, are something else, achieving an exhilarating sense of foreboding and unease – like the world was balanced on the precipice of insanity – that hits one’s nerves dead-center. A nocturnal aerial zoom across the rural Oklahoma landscape into a close-up of Ashley Judd, with the sound of whirring helicopter blades (or flapping insect wings?) growing in intensity, is the bravura starting point for this claustrophobic tale of Agnes (Judd), a drunk terrified of her menacing husband (Harry Connick Jr.) recently paroled from prison, and Peter (World Trade Center’s Michael Shannon), a socially awkward stranger who comes to stay in Agnes’ motel room home and who, it soon becomes clear, is a few cards shy of a full deck. What begins as a relationship of co-dependence – he providing her with kindness and protection, she offering him friendship in return – soon devolves into a romance of mass psychosis, as Peter convinces Agnes that they’re being ravaged by tiny, government-engineered flesh-eating bugs. A feverish montage of fluids, body parts and insect imagery casts Peter’s delusion as something akin to a highly contagious sexually transmitted disease. Yet as the film progresses ever further into crazy (including a third-act set entirely in a tinfoil-lined room), the material’s roots as a two-act stagebound piece become more frustratingly evident, and Friedkin’s direction – though still able to provide sharp visual complements for his story’s themes – loses some of its verve. Thankfully, though, the same can’t be said about the extremely out-there performances of Judd and Shannon, with the latter’s portrait of insanity so fervently committed and unleashed that it’s simply astounding.