“Equity” is bracing, witty and suspenseful, a feminist thriller sharply attuned to the nuances of its chosen milieu. In setting and mood, it bears some resemblance to J. C. Chandor’s “Margin Call,” which similarly infused sleek and sterile corporate spaces with danger and dread. But unlike that film or Adam McKay’s “The Big Short,” Ms. Menon’s movie is not about the system in crisis. It’s about business as usual. Which is to say about corruption, deceit and treachery.