The Thin Man opens in the workshop of Clyde Wynant, a tall, thin, wealthy inventor and businessman. Wynant, the father of two adult children, Dorothy and Gilbert, has recently left his wife after having a relationship with his secretary, Julia Wolf.

Dorothy and her boyfriend, Tommy, appear in her father's laboratory. They announce that they are engaged and will be married after Christmas. At the same time, Wynant mentions that he is going into hiding so he will not be disturbed while working on a new invention. He promises to be back in time for the wedding. This promise to return on time foreshadows Wynant's disappearance.

After placing his lawyer, Herbert MacCaulay, in charge of his affairs, Wynant discovers that fifty thousand dollars in government bonds is missing from his office. He had intended to give the bonds to Dorothy and Tommy for a...