Tereza learns soon afterward from one of the men she works with that the obnoxious man is with the secret police. The secret police function in several ways, Tereza’s coworker says. They spy and report back to their superiors, and they intimidate, so everyone knows who has all the power. The secret police also stage certain situations to incriminate others—like planting drugs in someone’s pocket or accusing them of rape.
Fear is the primary way in which the Russians and the communist regime maintain control over the Czechoslovakian people. Kundera later claims that nothing within a communist country can ever be trusted, from parades to politicians, and the obnoxious man is proof of this reality.
Tereza is suddenly convinced that the tall stranger was sent to trap and incriminate her. No engineer reads Sophocles, Tereza thinks to herself. She worries that he will say she slept with him and then demand money. Tereza’s coworker tries to assuage her fears. Nothing about her encounter with the tall stranger seemed suspicious, the coworker says, but she isn’t so sure.
Whether or not the tall stranger is really working with the secret police is never revealed, but Kundera certainly leaves this possibility open. After Tereza and the stranger’s afternoon together, he never reappears.