[3][4] The book's title appears halfway through the novel: "If one knew, he wondered, the facts, would one have to feel pity even for the planets?

Major Scobie lives in a colony on the west coast of Africa during World War II, and is responsible for local security during wartime.

Scobie is passed over for promotion to commissioner, which upsets Louise both for her personal ambition and her hope that the local British community will begin to accept her.

One of Scobie's duties is to lead the inspections of local passenger ships, particularly looking for smuggled diamonds, a needle-in-a-haystack problem that never yields results.

The captain says it's a letter to his daughter and begs Scobie to forget the incident, offering him a bribe of one hundred pounds when he learns that they share the Catholic faith.

Scobie declines the bribe and takes the letter, but having opened and read it—contrary to regulations—and finding it innocuous, he decides not to submit it to higher authorities, and burns it.

A letter he writes to Helen ends up in Yusef's hands, and the Syrian uses it to blackmail Scobie into sending a package of diamonds for him via the departing Esperança, thus avoiding the authorities.

Still, to placate his wife, Scobie attends Mass with her and receives communion in his state of mortal sin—a sacrilege according to Catholic doctrine.

Yusef says he will take care of the matter, which within a few hours ends up with Ali being killed by local teenagers known as "wharf rats".

Having gone this far down the path of ruin and seeing no way out, Scobie decides to free everyone from himself—including God—and plots his death by faking a heart ailment and getting a prescription for sleeping pills.

Louise tries to rationalise Scobie's suicide in relation to his Catholicism, to which the priest advises that no one can know what's in a person's heart or about God's mercy.

He appears to share the idea, floating around since Baudelaire, that there is something distingué in being damned; Hell is a sort of high-class night club, entry to which is reserved for Catholics only, since the others, non-Catholics, are too ignorant to be held guilty, like the beasts that perish.

[5][6]Orwell added: “But all the while—drunken, lecherous, criminal, or damned outright—the Catholics retain their superiority, since alone they know the meaning of good and evil.”[7] Literary critic William DuBois in the July 11, 1948 issue of The New York Times describes Graham Greene as “a profound moralist with a technique to match his purpose” and his protagonist, the policeman Scobie, as “a textbook case of a judge destroyed by his own sentences.”[8] DuBois offers the following passage to illustrate his characterization of The Heart of the Matter as a “parable” of a man who is “victim of his own acute kindness.”[9] Father Rank, the priest, visits Scobie's widow to offer condolences shortly after her husband's suicide: [Mrs. Scobie]: "He was a bad Catholic."

[10]DuBois adds: “Such is Mr. Greene's parable: the reader will search far to find another novel that explores that basic malaise in such clinical depth—and with such compassion.”[11] Writing in The Guardian, September 17, 2010, literary critic D. J. Taylor places The Heart of the Matter within the legacy of the “Catholic novels” that began to appear in the mid- 19th Century, “born out of the Tractarian movement” and part of the “Catholic tradition in English letters.”[12] Taylor adds that “the real impetus to the Catholic novel's mid-[20th] century rise was provided by converts: Evelyn Waugh, Graham Greene and, slightly later, Muriel Spark.”[13] Taylor offers this observation on the critical response to these Catholic-inspired works: Even Catholics found some of the complaints leveled at Waugh and Greene by their contemporary critics difficult to ignore.

Even to certain believers, Waugh's Catholicism was a symptom of his pursuit of "smartness", that zealous romanticizing of upper-class English life in which Brideshead Revisited (1945) positively revels.

Both Greene and Waugh believed that their characters' religious sensibilities gave them a dimension that most people in novels no longer possessed.

[14]Taylor reports that “any religious novelist faces…the absolute necessity of opening up the exclusive private club to which you belong to the non-members who don't wear its tail-coats or drink its claret.”[15] Literary critic Scott Bradfield in the March 10, 2021 The New Republic, considers The Heart of the Matter a “breakthrough” novel.

:[16] Greene achieved international fame by appealing to Catholics who found in it an expression of living in a post–World War II world where God didn’t seem to reward the faith they placed in Him.

[17]Observing that “Greene’s cynicism about the world—and the sufferings of humanity—came close to nihilism,” Bradfield quotes protagonist Scobie from The Heart of the Matter: “Point me out the happy man and I will point you out either extreme egotism, evil—or else an absolute ignorance.” Bradfield adds: “It’s hard to think of any similarly productive, commercial novelist today who speaks so vigorously against religious and political pieties.”[18] The novel was made into a film in 1953, directed by George More O'Ferrall and starring Trevor Howard and Maria Schell, and a TV film version was produced in 1983, featuring Jack Hedley as Scobie.