There be monsters in this gripping Swedish thriller. Unlikely monsters, but no less terrifying for that.

The second book to feature dogged police detective Joona Linna, “The Hypnotist” begins with the gruesome murder of a family. Linna enlists the help of Erik Maria Bark, an acute-trauma expert.

The detective wants the doctor to hypnotize the crime’s lone survivor, a 15-year-old boy who is severely wounded and in shock. It’s a desperate attempt to wrest eyewitness testimony from a catatonic patient.

Bark refuses because a previous incident had become a national scandal in Sweden, leading him to publicly vow he would never use hypnosis on a patient again.

But there are extenuating circumstances in this case, and Linna can be quite persuasive.

The weary doctor reluctantly agrees to hypnotize the boy, unleashing a scary chain of events that puts Bark, his wife and his son in mortal danger.

The married writing team of Alexander Ahndoril and Alexandra Coelho Ahndoril, using the Lars Kepler pseudonym, keep ratcheting up the suspense. Every time you think you have the situation figured out, the nightmare deepens and twists.

Their knack for shifting time frames and narrative perspective among the characters in short chapters will have you turning pages long after your bedtime.

While Stieg Larsson struggled with creating convincing bad guys (A thug with a rare medical condition that prevents him from ever feeling pain? Please.), the authors establish a murderer’s row of memorable villains in “The Hypnotist.”

The book navigates some murky psychological waters that may feel unfamiliar and ambiguous to American readers.

And there are some behaviors here that make no sense.

Here is Linna speaking to his boss’ superior, Carlos Eliasson, after bullying his way into taking over the case:

“Carlos looks down at his desk and clears his throat. ‘OK, you’re leading the preliminary investigation,’ he says. ‘The Tumba case is yours.’

“‘First of all, I want to hear one thing,’ says Joona. ‘Who was right? Who was right, you or me?’ ‘You!’ yells Carlos. ‘For God’s sake, Joona, what is it with you? Yeah, you were right — as usual.’“

Maybe that kind of office politics is a Nordic thing.

Of course, that’s one of the pleasures of reading imported fiction: sampling customs and behaviors in other cultures.

But the unsettling evil at work in “The Hypnotist” is the same all over the world.

David Hiltbrand is the author of three novels, most recently “Dying to Be Famous.”