Instruct: Classify the given review into positive or negative sentiment.
Query: an engrossing mystery

Out of necessity, Monk takes up an investigative crime assignment involving the theft of African ivory. Sounds straightforward enough, but there's more to the story, including of course the typical ingredients--murder, cover-up, and false identity. Gripping storylines, sprinkled with good relevent social commentary. Overall, full of action and mystery. Anne Perry's books are always to be recommended.