Passage of arms - Eric Ambler

In this classic thriller, two American tourists find more adventure than they bargained for when they get involved with Chinese gun smugglers and Muslim revolutionaries, learning first hand about the intrigue of the post-colonial world.

Greg and Dorothy Nilsen had wanted to go on an adventurous trip, see some of the more out-of-the-way places. But the cruise they were on was turning out to be a bore. So when the gracious Mr. Tan requests that Greg take a side trip to Singapore to resolve a bureaucratic detail involving a consignment of small arms, Greg is surprisingly receptive. All he has to do is sign some papers, he's told, and he'll be paid a handsome fee. And everything does go smoothly, until it comes to getting a check co-signed by the rebel leader