Deep in the African rain forest near the legendary ruins of the Lost City of Zinj an expedition of eight American geologists are mysteriously and brutally killed in a matter of minutes.

Ten thousand miles away Karen Ross the Congo Project Supervisor watches a gruesome video transmission of the aftermath: a camp destroyed tents crushed and torn equipment scattered in the mud alongside dead bodies all motionless except for one moving image a grainy dark man-shaped blur.

In San Francisco primatologist Peter Elliot works with Amy a gorilla with an extraordinary vocabulary of 620 "signs" the most ever learned by a primate and she likes to finger paint. But recently her behavior has been erratic and her drawings match with stunning accuracy the brittle pages of a Portuguese print dating back to 1642 . . . a drawing of an ancient lost city. A new expedition along with Amy is sent into the Congo where they enter a secret world and the only way out may be through a horrifying death ...