This slug like parasite is actually a symbiote. After attaching itself to a warmblooded host, it feeds off that being. However, its tenticles, growing under the skin, act as secondary nerves, increase the victims nerve responses.
It looks like a cook's book. It is a cook's book. It is also where the cook, who happened to be a master spy, encoded all his secrets and contacts. The book has innocently fallen into your group's hands. Everyone wants it, and many are not subtle or peaceful in their attempts.