On a routine intelligence gathering mission in Tehran, Jack Ryan, Jr, has lunch with his oldest friend, Seth Gregory, an engineer overseeing a transcontinental railway project. As they part, Seth gives Jack a key, along with a perplexing message. The next day Jack is summoned to an apartment where two men claim Seth has disappeared-gone to ground with funds for a vital intelligence operation. Jack's oldest friend has turned, they insist. They leave Jack with a warning: If you hear from Seth Gre