UNKNOWN by Mari Jungstedt is the third in a series of police procedurals set on the scenic island of Gotland in Sweden. Jungstedt's hero, the grumpy Inspector Knutas, investigates the gruesome killing of a horse on the island, travelling to rural Gotland from Visby, the only city on the island.

Whilst Knutas and his team investigate, we also see events unfold through the eyes of Martina, a Dutch archaeology student. She is in Gotland for the summer to take part in a dig unearthing Viking treasures. Martina has a secret boyfriend, and tries to throw off a sense that someone is spying on her. Johan, the journalist present in earlier novels in the series, is also present on Gotland, as a local news correspondent for Swedish TV. He is somewhat distracted by the impending birth of his first child by his lover, Emma, but still manages to undertake some spadework. When a human body is found, and more horses are killed, media interest snowballs, and Knutas and his team struggle to find the perpetrator. Meanwhile Johan does his own work on the cases, investigating the theft of Viking artefacts on the island, in case this ties in with the human and animal deaths.

UNKNOWN has a strong sense of location, providing a sunnier more relaxed and touristy image than is common in Scandinavian crime fiction. Although the first human death doesn't occur until about 200 pages into the book, the pace and tension are well-maintained, Jungstedt grabs the readers, attention, drawing you into the events and characters surrounding the dig and the police investigation into the animal deaths. Characterisation is nicely done; the characters of Knutas and his colleagues and of Johan are nicely rounded, taking in both their professional and personal relationships, in particular the blooming relationship of Johan and Emma.

There are two small disappointing notes in the novel; the identity of the perpetrator feels a bit of a cheat, reliant on information not available to the reader, and the italicised insight into the mind of the perpetrator has become somewhat of a cliche, and doesn't really add to the novel. Overall UNKNOWN is a genuinely gripping read, and the plotting is rather better than that of earlier books in the series.