As in Michael Crichton's Congo--but to far less entertaining effect--the gimmick in this otherwise routine suspense is the involvement of gorillas who have learned to communicate with homo sapiens. The apes in question: Joey, Winston, and Fran--who've been taught sign language by Abbie Guisbourne at the Burundi Primate Research Center. But, while cutesy scenes of Abbie and the gorillas pad out the novel's first half, a dark plot is brewing that will disrupt the Center's pleasant status quo: the local Popular Liberation Front, determined to gain the release of an imprisoned star-terrorist slated for execution, plans to kidnap American Abbie and her staff as hostages. So sensitive, non-violent guerrilla Bunkeya impersonates a courier, gaining admission to the Center and paving the way for the actual kidnap, across a lake to a hideout in Zalre. And when Abbie's new friend Evan Ogilvie (of the US Embassy) finds Abbie and five others missing, the only clues come from the gorillas--who sign-language the word ""crocodile"" (symbol of the Liberation Front). Eventually, however, the Front announces its demands, Evan (with craggy British professor Mic Fielding) figures out where the hideout is, and a rescue mission is planned (using the gorillas to distract the bad guys) . . . while hostage Abbie is nearly killed because of schemings by ambitious guerrilla Mpinga. But when the hideout is finally stormed, Abbie has disappeared--caught between good guerrilla Bunkeya and bad guerrilla Mpinga--and it's up to the gorillas to find her and save her. . . . Readers who've missed the many fiction and non-fiction accounts of gorilla language-training may enjoy the detailed sequences here; and there's a bit of appealing comedy in mild-mannered Evan's encounters with the apes. Thriller fans, however, will find this a genial but slow-moving and tensionless adventure, with little real sense of the African terrain and not a single real surprise along the way.