The Fifth Woman by Henning Mankell

Sixth in the Kurt Wallander series.

In an African convent, four nuns and a unidentified fifth woman are brutally murdered--the death of the unknown woman covered up by the local police. A year later in Sweden, Inspector Kurt Wallander is baffled and appalled by two murders. Holger Eriksson, a retired car dealer and bird watcher, is impaled on sharpened bamboo poles in a ditch behind his secluded home, and the body of a missing florist is discovered--strangled and tied to a tree. The only clues Wallander has to go on are a skull, a diary, and a photo of three men. What ensues is a case that will test Wallander’s strength and patience, because in order to discover the reason behind these murders, he will also need to uncover the elusive connection between these deaths and the earlier unsolved murder in Africa of the fifth woman.