A young writer goes to Wiesbaden to write about gambling and gamblers, only to ultimately become a compulsive gambler himself. Losing all his wealth, as well as his moral fibre, he commits the ultimate degradation of robbing a church poor box in order to feed his compulsion.

A famous psychologist, Margaret Ford, decides to try to help one of her patients get out of a gambling debt. She visits the bar where Mike, to whom the debt is owed, runs poker games. He convinces her to help him in a game: her assignment is to look for "tells", or give-away body language. What seems easy to her becomes much more complex.