Kahaani is an absolutely remarkable film for three reasons. First, it is the tautest, most involving thriller to have come out of Hindi cinema in years. Second, it is a stunningly shot city film, made inestimably more memorable by the simple move of stepping out of supremely overused Mumbai streets and increasingly familiar Delhi locations into a startlingly cinematic Kolkata. And third, it contains another bravura performance from the marvellous Vidya Balan, stepping back into the arc lights, even...