The novel starts with an abrupt end to an expedition sent by Earth Resource Technology Services Inc. in the dense rain forests of Congo when the team is attacked and killed by an unknown creature and all contact with them is lost. The expedition, searching for deposits of valuable diamonds, discovered the legendary lost city of Zinj (in Arabic "Zinj" or "Zanj" refers to the southern part of the East African coast). A video image taken by a camera there, and transmitted by satellite to the base station in Houston, shows a peculiar race of grey haired gorillas, to be responsible for the murders.
Another expedition, led by Karen Ross, is launched to find out the truth and to find the city of Zinj, where there are believed to be deposits of a certain diamond, type IIb, which are naturally boron-doped and thus useful as semiconductors, though worthless as gemstones. This time the searchers bring along the famous White African mercenary Munro, as well as a female gorilla named Amy, who has been trained to communicate with humans using sign language, and her trainer Peter Elliot. Time is of the greatest essence, as a rival consortium of Japan, Germany, and Holland has also set off into the jungle after the diamonds, turning the entire expedition into a race to the city of Zinj. Unfortunately for Ross and her team, the American expedition encounters many delays along the way, including plane crashes, native civil wars, and jungle predators.
A film adaptation was released in 1995.
This book provides examples of:
- Abandoned Camp Ruins: When the protagonists' expedition arrives to the place where the missing E.R.T.S. expedition they were sent to find was camped, the narration notes that in the weeks in between the missing team's last contact and the protagonists' arrival the whole site has been Reclaimed by Nature and cleaned by the Killer Gorilla tribe who killed the team, and aside from a couple of gadgets there is no trace left.
- Always a Bigger Fish: Munro goes on a punitive expedition to wipe out the killer gorillas, finds several of them and is about to open fire when he realises the entire mountain in swarming with them. He beats a hasty retreat.
- Bittersweet Ending: Ross, Elliot, Amy, and Munro escape the Congo with their lives, but that's about all they escape with, as most of the porters they brought with them are dead, and the eruption of Mukenko has buried the Lost City of Zinj, Ross' diamonds, and Elliot's dreams of introducing a new species of gorilla to the world under almost half a mile of lava in one fell swoop. The epilogue gives a little more sweetness to their future: Ross resigns from ERTS and eventually marries a fellow scientist, Elliot sees Amy begin to fully assimilate into a mountain gorilla troop, Amy bears a child to whom she can teach her own sign language (which Elliot witnesses for himself), and Munro is able to return to his old lifestyle after selling a handful of blue diamonds on the market for a handsome profit.
- Cannibal Tribe: The team has to constantly avoid a cannibalistic tribe of natives (the Kigani) who are at war with the Mobutu government. Partly because they were cannibals, but mostly because Mobutu was a vicious dictator running a People's Republic of Tyranny and he didn't like that said tribe was ignoring him. Nor does it help that the general in charge of battling the tribe, Ngo Muguru, is said to be just as unpleasant as any one Kigani.
- Chekhov's Volcano
- Closed Circle: What the Lost City of Zinj becomes to the expedition, because of sheer distance from any help, a rival expedition's jamming and eventually sun spots and atmospheric phenomena kills all satellite communications, and because the Killer Gorilla tribe has closed off their escape route.
- Contrived Coincidence: The fact that ERTS is one of the sponsors of project Amy becomes this, not only because of the involvement of apes in the destruction of the first team, but also because it is eventually revealed that Amy was born near Zinj and her mother was killed by the grey apes.
- Corporate Warfare: Presented here as a sort of Cold War by proxy.
- Darkest Africa
- Denied Food as Punishment: In an early chapter, Elliott says that he sometimes punishes Amy's misbehavior by sending her to bed early without her usual peanut butter and jelly snack. Subverted in that while it is a punishment, it's just a tasty snack that she enjoys, and she is still getting a full meal - basically, she's still getting dinner, just not any dessert afterwards.
- Diurnal Nocturnal Animal: Played with. The gorillas always attack at night, but a very large group is shown feeding during the day.
- End of an Era: Of the typical Jungle Opera, or at least from Munro's point of view, with him mentioning how expeditions are depending greatly on technology to plot their course (and even forcing him to learn computer programming language) and solve their problems. Elliot also believes this a bit, quoting Livingstone and Stanley's expeditions on his thoughts.
- Enhance Button: Zig-Zagged Trope: the hunt to enhance a piece of footage that displays one of the killer gorillas storming the first ERTS camp requires specialised computer programs (some of which need to be run to counteract a degradation of the footage that the previous program unwillingly created) and a long amount of time, and Ross needs to run several programs to make sure that the resulting slightly-more-clear image is real, as well as needing to convince Travis of this (the resulting picture still looks bad enough that Travis thinks at first it's an "easter egg" from a rookie programmer that Ross unknowingly triggered). It is the speed and efficiency of Ross pulling this off that helps her convince Travis to send her as the needed "console hot-dogger" for the second expedition.
- Eye Scream: The leader of the first expedition is looking for his friend when something plops next to him. He picks it up and realises he's holding a severed eyeball.
- Fun with Acronyms: W.E.I.R.D. (the defensive package of the expedition), S.D.T.A.G.W ("Some Damn Thing Always Goes Wrong", written on a plaque on Travis' desk).
- Gentle Gorilla: Amy was raised in captivity by humans and trained to communicate via sign language. She's very friendly and docile, and acts as an interpreter between the humans and the Killer Gorillas.
- Hired Guns: Munro is a famous White African mercenary.
- Hollywood Natives: The Kigani tribe run around with spears, bows, face paint and practice cannibalism constantly. They also throw their poop like monkeys for some bizarre reason.
- I'm a Humanitarian: The group has to constantly evade a tribe fighting the Mobutu government.
- Ice Queen: Ross.
- Jungle Opera: An attempt to update the trope.
- Killer Gorilla: On the way to the city of Zinj, Karen Ross's team has to contend with a group of deadly gorillas. Played with, in that the gorillas are not inherently aggressive, but were trained that way by the former inhabitants of Zinj, and they have been teaching themselves this behavior through succeeding generations.
- Misapplied Phlebotinum: The compression algorithm used for voice communication is impressive even for today: real-time audio encoding and decoding on a general-purpose computer somewhere between last-generation 8-bit Atari XE and lowest-end IBM PC. But the way they use it, a text chat would've been faster and more convenient.
- Parachute in a Tree: This happens to Elliot when the team parachutes into the jungle. Fortunately, he's only four feet above the ground, so he can undo his chute and jump down without getting hurt. It's still a very unnerving experience for him since this is the first time he's ever jumped out of a plane.
- Rock Beats Laser: Averted HARD. The Kigani tribe rebelling against Mobutu's government is still at a stone age level of technology with bows, arrows, and spears. It is made VERY clear that there primitive weapons stand no chance in hell against the modern attack helicopters, RP Gs, and assault rifles wielded the Zaire army sent to fight them. This is made even more clear at the end when the protagonists, reduced to only four people (and one gorilla) still manage to hold off and decimate an entire war party of Kigani themselves, armed only with assault rifles (though they quickly run low on ammunition and are forced to escape before the next war party is send against them).
- Sentry Gun: One of three pieces of the expedition's W.E.I.R.D. package (alongside a portable electrified fence, Night-Vision Goggles and Frickin' Laser Beams in designator-rifle-mode for the guns). Tripod-mounted, portable, silenced, capable of detecting heat or attack laser-designated targets. They unfortunately (and quickly) become Too Awesome to Use because of their immense firing rate eating too much ammo.
- Team Pet: Amy fills this role, yet she's very human in a way.
- The Worm Guy: Two members of the expedition are this: Peter Elliot (because of his knowledge of gorilla behaviour) and Karen Ross (who is a self-proclaimed "console hot-dogger" and the one with the skills to run the expedition's technology and analyse its data faster than it would take if it was sent back to Texas-and later because there is no communication at all).
- Too Dumb to Live: Despite being a trained geologist, Ross's psych profile states she has a habit of cutting corners and acting rashly when her goal is in sight. At the end, she almost gets the entire team killed when she ignores Munro's warning about how dangerous it is to set off explosive charges near an eruptive volcano.
- 20 Minutes into the Future: The novel, which can be disconcerting as it's also set around the collapse of the Amin regime (current events at the time it was written).