William Monahan, who has written screenplays for some terrific movies--The Departed among them--is fast on his way to becoming the smartest, wiliest indie director no one has heard of. In 2010 his scrappy, '60s-inflected thriller London Boulevard, with Keira Knightley and Colin Farrell, disappeared, unfairly, with barely a trace. Now he brings us the wicked noir comedy Mojave. Garrett Hedlund's Thomas, a hugely successful but very depressed star, treks to the desert to find enlightenment or solace or both. There he's joined, around his cozy little he-man campfire, by scruffy autodidact drifter Jack (Oscar Isaac), who's fond of Shakespeare, the Bible and messing with people's heads. When Thomas asks what he "does," Jack replies, "I fall upon travelers. People come out to the desert, they get fallen upon by thieves.…