Book excerpt: Yacht Rosa was due to leave the San Francisco harbor in two hours.We were going on some mysterious cruise to the South Seas, the details of which I did not know.""Professor George Berry, the famous zoologist, and myself are going to do some exploring that is hazardous in the extreme,"" Stanley had said. ""For purely mechanical reasons we need a third. You are young and have no family ties, so I thought I'd ask you to go with us. I'd rather not tell you what it's all about until we are on our way.""