Faceless Killers is the story of divorced police detective Kurt Wallander's quest to bring to justice the murderers of an elderly farming couple. Wallander must deal with depression following his divorce, his daughter's emotional and physical distance, and his own problems with food and drinking. Meanwhile, he must cope with a leak to the media that the killers were foreign causing a string of anti-refugee violence, including another senseless murder. Wallander ultimately brings the killers to justice through painstaking police work.

As the novel begins, Maria and Johannes Lövgren are found at their rural farm. Johannes has been gruesomely killed, and Maria has been strangled with a noose and is barely alive. Detective Kurt Wallander is called in to investigate. Wallander's wife has recently left him, and he's lost touch with his daughter since she tried to commit suicide four years ago.

Maria Lövgren dies at the hospital, and her last word is "foreign," something Wallander tries to keep from the police. However, the information is leaked to the press, and soon white supremacist groups are becoming violent. Meanwhile, Wallander learns that Lövgren secretly had a fortune stashed away and made large payments to his former mistress, the mother of his illegitimate child.

Wallander is trying to track down Lövgren's mistress and son when a Somali refugee is shot and killed. Wallander's investigation is sidetracked as he interviews witnesses to find the killers. He discovers that a Citroën was involved with the crime, and an ex-policeman reports his Citroën stolen. Wallander, suspicious, follows the ex-policeman and uncovers the murderer, who dies in a high-speed chase.

Meanwhile, Wallander fails to reconcile with his wife and becomes attracted to the new public prosecutor, a married woman from Stockholm. They slowly edge into a relationship over the course of the novel. Wallander learns that his daughter is dating a Kenyan medical student and considering college, and Wallander and his daughter, too, begin to re-forge a relationship. Wallander's father begins becoming senile, and Wallander has to put him in the hospital for several days and then get a daily helper to come take care of him. His closest friend on the police force is diagnosed with cancer as well.

When Wallander returns to the Lövgren murders after solving the murder of the Somali refugee, he tracks down the illegitimate son, who looks like a promising suspect. The son mysteriously paid of a large gambling debt; however, he is cleared. The money came from the sale of a car, and the son has an alibi for the night of the murder. The investigation stalls until Wallander makes a connection to two foreigners who were at the bank when Johannes Lövgren was withdrawing money. He finally tracks the men down and solves the murder after seven months of painstaking investigation.