Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Worth dipping into.

Like Poul Anderson's science fiction (although as retold by Günter Grass), this well-researched novel about the Holocaust depicts the moral torments that an agent of the future faces as he derails a group of altruistic time travellers. The groups' plan is to alter history by attacking Nazi death camps and freeing the inmates. Although the brutal contrast of life in Auchwitz retains an intensity far beyond the high-tech milieu of the pursuing time police, it's to the writer's credit that the book's most vivid elements are based in history