A missile is launched from Cape Canaveral, but it runs wild and goes down in the Caribbean area. The missile must be found because it contains a newly developed electronic recording device in its nose cone -- a mechanism that must not fall into foreign hands. The Bureau assigns the task of locating the device to Mel and Bill. Traveling as magazine photographers, with Mel conveniently hidden inside a rolleiflex camera, Bill and Miss Brown fly south to El Porto -- a Central American town from which has come reports of "shooting stars and flying saucers." They locate the missile crater but the recording device is gone. It had been found by an eight-year-old boy named Pedro who refuses to give it up. Mel decides some applied child psychology is in order and proceeds to turn Pedro's donkey, Pepe, into a talking animal. The child, wide-eyed with amazement, agrees to give back the device on the promise that he will receive a gift in its place. The plan goes awry when Garcia, the local coffee plantation owner, and his henchman, Ortiz, step onto the scene. Garcia, through his business connections, has international contacts who have offered him a huge sum for the device. However, Bill manages to outwit Garcia -- with a noble assist from Mel -- before the device can be shipped down river in some coffee bags. And Pedro, momentarily disillusioned because Pepe will no longer talk, finds that it does pay to believe in a promise -- even when it comes from the mouth of a donkey.