What is the purpose of detective fiction? For Ausma Zehanat Khan, it’s a perfect tool for getting us to see — really see — problems that are right before our eyes: humanitarian crises and war crimes, for instance. Khan, a former immigration lawyer and editor of the now-defunct magazine Muslim Girl, has created a mystery series starring a Muslim police detective, who along with his partner, has not only confronted anti-Muslim hate crimes in Canada, but has also roamed farther afield to ravaged places like Sarajevo, Iraq and Syria to look at evils the world would rather forget.

“A Dangerous Crossing,” by Ausma Zehanat Khan (Minotaur/Minotaur)

“A Dangerous Crossing” is the fifth novel in the series, and it tackles a timely subject: the plight of Syrian refugees. According to the United Nations High Commissioner for Refugees, more than 5 million Syrians have been driven from their country or displaced internally since the start of that country’s civil war in 2011.

Khan’s mystery opens in a refugee camp in on the Greek island of Lesvos (pronounced as “Lesbos”). Audrey Clare is a case worker from Canada who is helping resettle refugees through a nongovernmental organization (NGO) she runs called “Woman to Woman.” Audrey is on the beach at night with other volunteers scanning the waves for overburdened boats carrying their desperate human cargo of refugees. She tells a young man named Ali that she’s returning back to the headquarters of her NGO (a tent in the refugee camp) to meet an Interpol agent who wants to talk to them both. Readers are left in the dark about the reason for this conversation. When Audrey leaves the beach, Ali gets delayed. When he finally makes his way back to the tent, he hears gunshots. He rushes inside to find the corpses of that Interpol agent and a male refugee.The murder weapon is Audrey’s gun; Audrey has vanished.

Cut to Ottawa, where Inspector Esa Khattak and his partner, Sergeant Rachel Getty, are attending an official reception. At the end of the evening, they will be asked by Audrey’s brother, Nathan Clare, to find her and solve the murders. Nathan is a wealthy Canadian philanthropist who helped bankroll her NGO. Understandably, Nathan is worried about his sister, but her disappearance and the murders also could have a political impact: They could undermine the young prime minister’s controversial efforts to fast-track refugee resettlement in Canada. The fact that Nathan Clare is Khattak’s oldest friend, as well as the object of Getty’s romantic longings, adds even more urgency to the case.

Overwhelmed? I was, too. The personal histories of Khan’s characters are so enmeshed that tracing back their connections is like trying to untangle a hair ball. We learn, for instance, that Khattak’s physician sister, Ruksh runs a clinic for new Syrian arrivals to Canada that partners with Audrey’s NGO. Meanwhile, Khattak’s late wife’s best friend, a lawyer named Sehr Ghilzai, enters the fray because she handles refugee claims for Audrey’s NGO. Sehr also has the hots for Khattak and is jealous of his easy rapport with Getty.

I used to think Elizabeth George’s Inspector Lynley series was unrivaled when it came to suspense stories grinding to a halt while the characters attended to their bruised feelings and unscratched romantic itches, but Khan’s mystery has set a new gold standard for backstory complications. Adding to the confusion is the fact that Khan is not as deft as she could be in the skill that every series mystery writer must master: namely, speaking to two audiences at once — those who have read all the novels in the series and those readers who are starting with the latest. For example, Khattak’s sister is barely speaking to him because of an offense dating from earlier in the series that’s alluded to here but not described.

The author Ausma Zehanat Khan (Ausma Zehanat Khan/Ausma Zehanat Khan)

The obscuring effect of all this cryptic personal detail is regrettable, because when Khan concentrates on the suspense plot, she spins an exciting story that enlightens as much as it entertains. Khattak and Getty’s investigation takes them to Greece, then close to the Turkish-Syrian border, and then to the Netherlands and finally back to Lesvos, where the mystery began. Khan writes with a vivid sense of immediacy whenever she’s describing the refugee situation. Here’s a scene where Getty transforms from being a witness to the refugee boats landing on Lesvos to a rescuer:

“She ran into the water, her steps slowing as they met the drag of the waves. She took the opposite side of the dinghy, using her upper-body strength to help . . . pull it in. . . . Even this limited attempt was wearing at her muscles. . . . A young woman whose lips were blue unclutched her freezing hands from the baby in her lap. The man beside her . . . reached down and passed the baby to Rachel. . . . The baby’s skin was cold, its eyes closed.”

“A Dangerous Crossing” urges readers to consider not only the obvious natural hazards faced by Syrian refugees but also the evils perpetrated by human predators who lurk in the shadows. Finding a solution to those evils may be well beyond the reach of Khan’s master detectives, but her complex tale helps us to, at the very least, see them more clearly.

Maureen Corrigan, the book critic for the NPR program Fresh Air, teaches literature at Georgetown University.

a dangerous crossing

By Ausma Zehanat Khan

Minotaur. 352 pp. $25.99