The Firm is a 1991 novel by the American attorney turned novelist John Grisham. It is an example of the legal thriller and one of many popular books he wrote in the 90's. It was adapted into a 1993 film directed by Sydney Pollack and starring Tom Cruise and Gene Hackman.
As to whether it is more character or plot driven, I think that it is an open question as almost all novels are some combination of the two. That said, I would argue that, like many popular genre novels, it relies more on plot to engage the reader than on its character.
A brief synopsis of the story will demonstrate Grisham's strong use of plotting. The novel is about Mitch McDeere, a young lawyer just out of Harvard, who settles at a small firm in Memphis. Shortly into his time at the firm, he begins to suspect, after the mysterious death of two of his co-workers, that there is something unusual about his new job. It turns out that it is a front for a mob family, and McDeere now founds himself wrapped up in a tense and potentially lethal situation—one exacerbated by an FBI investigation and his close relationship with an older lawyer whom he doesn't want to betray.
Still, you probably wouldn't continue reading a book if you weren't interested in the characters, and McDeere is one of Grisham's drawn characters; he's smart and ambitious but finds himself in a state of conflict, and it is conflict, of course, that is the engine of drama.