The past is a fire that never stops burning.

At a desolate rest area in Kronviken, a woman's body is found - severely burned, unrecognizable, her identity erased by a melted blue cap. For Detective Inspector Maria Wern, it is a gruesome puzzle. For her colleague, Per Arvidsson, it is the beginning of a journey into a past he didn't know he had.

While Maria hunts for a connection to a local arsonist, Arvidsson discovers a life-altering secret: he was adopted, and his biological sister, Pernilla, is still out there. But as he reunites with his long-lost family, he finds himself drawn into a world of fractured memories and childhood traumas that refuse to stay buried.

In the shadows of the investigation stalks Pyret-a woman whose life was forged in the flames of a horrific childhood tragedy. When she witnesses a brutal assault that mirrors her own dark history, she is forced into a deadly game of cat and mouse. Pyret holds the key to breaking Maria's case, but coming forward means risking the carefully constructed life she has built on the ashes of the past.

As Maria and Arvidsson's investigations collide, they discover that some childhood refuges are actually prisons - and that a killer is using a shared history of fire and blood to settle an ancient score.

In this chilling psychological thriller, author Anna Jansson proves that the most dangerous secrets aren't the ones we keep from others, but the ones we tell ourselves to survive.

'Black Butterfly is beyond a doubt Anna Jansson's most cleverly constructed novel.' - Nerikes Allehanda / SWE