Unknown, Byy Mari Jungstedt, translated by Tiina Nunnally

Decapitated equines have had a Mafiosi context until now: who could forget that pillow surprise in The Godfather? Mari Jungstedt's novel takes the image into a different setting, while retaining its iconic horror. The Swedish island of Gotland, with its mixture of hard-working locals and wealthy incomers, is enjoying its innocent summer when two young girls discover that a beloved pony is no longer available to ride. In ancient Scandinavia, a horse's head stuck on a pole was a fearsome threat – but where is poor Pontus's head, and whom will it threaten?

Things go rapidly downhill as animal abuse turns into a murder investigation. There's an archaeological dig taking place, and a visiting Dutch student is found hanging from a tree with strange markings on her skin. Detective Superintendent Anders Knutas finds himself caught in a complex web that involves a group of archaeologists, stolen treasure and a psychopath stalking the island.

There's also the possibility of an unpleasant inheritance from the Viking past: the "threefold death", where a victim is hanged, stabbed and drowned, economically placating three different gods. And maybe some sophisticated modern professionals want to revert to an ancient religion involving buckets of chicken's blood. The tiny island is seething with a heady brew of historical traditions, jealousies and murderous passions.

In her third novel featuring Knutas and television reporter Johan Berg, Jungstedt's plotting skills have developed to create satisfying entanglements, and her main characters are now richer personalities. The members of the archaeological excavation are persuasively delineated, while Berg's romantic entanglement is treated with depth and subtlety. There is plenty of tension as reporter and detective discover bloody rituals and get closer to the killer. I did worry about how much farmyard life there was left on Gotland, but no doubt it can re-stock in time for Jungstedt's next thriller.