Congo by Michael Crichton

From the bestselling author of Jurassic Park, Timeline, and Sphere comes a gripping thriller about the shocking demise of eight American geologists in the darkest region of the Congo.
 
Deep in the African rain forest, near the ruins of the Lost City of Zinj, a field expedition is brutally killed. At the Houston-based Earth Resources Technology Services, Inc., a horrified supervisor watches a gruesome video transmission of that ill-fated group and sees a haunting, grainy, man-like blur moving amongst the bodies. In San Francisco, an extraordinary gorilla named Amy, who has a 620-sign vocabulary, may hold the secret to that fierce carnage. Immediately, a new expedition is sent to the Congo with Amy in tow, descending into a secret, forbidden world where the only escape may be through the grisliest death.