Dan arrives at a book collector’s office and exchanges sign and countersign. Dan picks up his tape and is briefed on Henrik Durvard, who has seized power in Lombwanda. He has taken a $30 million diamond from the tribesmen who found it and plans to take over independent tribal areas in his country. The IMF must recover the diamond.
Dan assembles the usual team plus former Scotland Yard inspector Ian McCloud and diamond expert Hans Van Meer. In the briefing, the group examines a photo of the diamond Van Meer gives Cinnamon a diamond necklace and Barney confirms the machine has arrived in London. They’ll be meeting McCloud in London and Durvard arrives the day after tomorrow.
In London, Van Meer, Dan, and Rollin arrive at a diamond house at the same time as Durvard, who brings a small sample. Cinnamon is also present and watches as they confirm the stone’s authenticity, and the guys get a photo. Durvard announces that bidding will start in 72 hours and as he leaves, Cinnamon asks to meet with him, with an offer for half a million dollars. Van Meer starts working on making a fake of the stone and Rollin goes to meet Cinnamon at Durvard’s hotel. A masked Barney and Willy intercept Durvard’s car, force him to pull over, and steal Cinnamon’s necklace. Cinnamon insists they continue to Durvard’s hotel.
At the hotel, Rollin meets with them as Durvard plays with his pet cat. He and Cinnamon offer to top the highest bid and want him to announce the discovery of another diamond find. Durvard agrees to consider it and they leave, as he wonders why Cinnamon wouldn’t go to the police.
Van Meer finishes the fake diamond, and gives it to Barney who brings back the necklace then goes to the hotel where Willy is next to Durvard’s room. Barney cuts into Durvard’s room through the electrical outlet and pumps knockout gas into the room, taking out Durvard and his guard. Barney then removes the outlet plate and uses an extendible arm to put a mirror on the bedstand next to Durvard. He the uses the arm to get at the box Durvard carries that holds the sample diamond. They switch it for the fake and Barney prepares to put it back, but Durvard’s cat comes in and starts toying with the arm. Barney lures it over to the outlet and sprays gas in its face, knocking it out. Barney then finishes the switch and closes everything back up.
Rollin and Cinnamon, along with Dan, meet with Durvard who figures they want to buy a source of diamonds rather then the diamond itself. McCloud arrives with Cinnamon’s diamonds, but says he hasn’t found the thieves yet. After McCloud leaves, Durvard inspects the stones and realizes that two of them are identical. He spots the carbon stains on Dan’s hands and concludes they’ve discovered a way to synthesize diamonds. Over Dan’s objections, Rollin agrees to show Durvard the synthesizing process. They produce their own, and then Durvard insists they make a duplicate of his (now fake) stone. Dan does so with his secret process, and Rollin uses a bit of sleight of hand to switch the real stone with the fake, then crushes the fake before Durvard can check both stones simultaneously.
Durvard tells them to move the entire synthesizing process to his country and they’re forced to agree. Dan, Rollin, and Willy fly to Lombwanda and set up their equipment in a high-security warehouse. Willy gets a pass from Durvard to bring in more equipment while Barney emerges from a secret compartment. Durvard has the Lombwanda Diamond brought in for duplication. They begin the (fake) duplication procedure while Willy and Barney cut through the outside wall behind the machine. Barney then extracts the real diamond from the fake machine and hands it off to Willy. The machine starts to run out of control and Rollin calls Dan back behind the machine. They turn on a tape recording of a pre-recorded conversation then go out through the hole. The machine explodes, killing Durvard, while the team drive out using the pass and make their escape.
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