Drawing upon his experiences as a native of the Deep South and as a lawyer, John Grisham created in The Firm a chase and suspense adventure involving the Federal Bureau of Investigation (FBI), the Mafia, and a young attorney coming to terms with the reality of life in the world of big business and big money.

The Firm is divided into forty-one short chapters. It is written from the third-person point of view, principally from the perspective of Mitchell McDeere; parts of the book are told from the viewpoints of other characters.

When Mitchell McDeere completes Harvard University Law School in the top five of three hundred graduates, he is much in demand, but no offer matches that of the firm of Bendini, Lambert, and Locke in Memphis, Tennessee. In addition to a starting salary of eighty thousand dollars a year, he is assured payment of his student loans, an expensive automobile, a low-interest home loan, and incredible perks for good work. When Mitchell and his wife Abby settle in their new house in Memphis, he is caught up at once in preparing for the state bar exam, which he passes a few months later with the highest score in the state.

Soon Mitchell is working twelve or more hours a day, and his home life suffers. The senior members of the firm are pleased, however, and his career seems well on its way to success, for he does not know the dangerous secret the senior partners are hiding from him and other young lawyers. The firm is a front for the Morolto Mafia family in Chicago and is involved in tax frauds and other illegal operations involving millions of dollars.

Satisfied with the firm despite the long hours, Mitchell is shocked when he is approached in a downtown restaurant by FBI agent Wayne Tarrance and told of the firm’s illegal activities and Mafia connections. Several deaths of younger firm members in recent years were in fact murders, not accidents and suicides as had been reported. Tarrance endeavors to recruit Mitchell in a plan to expose the firm.

At first reluctant, even frightened, by such a dangerous scheme, Mitchell begins to become disillusioned when he discovers that both his car and his house have been bugged. Two senior members of the firm, Oliver Lambert and Nathan Locke, informed by their security agent DeVasher of taped conversations between Mitchell and his wife, are increasingly concerned about their new “star.” To assure his compliance with their plans, they send him with Avery Tolar, his mentor in the firm, to Grand Cayman for business and relaxation. There, a young woman in their employ seduces Mitchell, who has previously been totally faithful to his wife.

Subsequent contacts with the FBI, both in Memphis and in Washington, and his growing suspicions about the mysterious deaths lead Mitchell to contact a private investigator, Eddie Lomax. Eddie is a friend of Ray, Mitchell’s brother, who is in prison. Eddie agrees to investigate the firm, but before he comes up with any significant information, he is murdered. Mitchell resolves to divorce himself from the firm and its illegal activities, and together with Eddie’s secretary and sometime lover, Tammy Hemphill, who wants revenge for Eddie’s death, he conspires to outwit the firm.

While devoting ever more hours to his work, Mitchell is at the same time meeting with the FBI agent, who promises him a new life for his cooperation; Mitchell also gathers material for his own purposes. Meantime, DeVasher, increasingly suspicious, shows the young attorney compromising photographs made of him with the young woman in Grand Cayman; DeVasher threatens to send the pictures to Abby McDeere should he find any cause whatever. Though fearful that Abby will discover his infidelity, Mitchell continues in his dangerous plan. With the aid of Tammy Hemphill, he manages to photocopy confidential files from the firm and place them in storage. On Grand Cayman, Tammy seduces Avery Tolar, puts knockout drops in his drink, and steals his keys to the storage files in the firm’s island condominium. Abby McDeere has secretly flown to Grand Cayman to meet Tammy, and the two copy all the incriminating files, which Tammy then takes to Nashville.

Through a plant in the FBI, the firm learns of McDeere’s defection and plans his destruction, but Mitchell’s scheme progresses. At his insistence, the FBI arranges for his brother Ray’s escape from prison. When Mitchell receives a coded warning from the FBI that the firm knows everything, he sends a message to Abby through Tammy and flees Memphis. He and his wife rendezvous on the Gulf Coast, where they videotape many of the documents shipped to them by Tammy and plan their escape.

For days, they are pursued by both the FBI and the Morolto Mafia family before their escape arrangements are completed. Barry Abanks, a scuba instructor from Grand Cayman, and a man known only as George, himself a fugitive from the law, arrive in George’s boat to pick up the McDeeres, who are armed with fake identification and the videotapes of the documents, and speed them away to the Caymans. The original documents are left in the motel for the FBI, but the McDeeres keep the videotapes as security. The novel ends with Mitchell and Abby drinking rum punch on a tropical beach and planning their future as fugitives.