Man can move easily enough in the three dimensions of space - why not the fourth: Time? An intriguing after-dinner conversation takes an unexpected turn when the host produces a small machine, which promptly disappears into thin air. It has been sent into the future, he says. Or maybe the past. As his skeptical guests try to fathom what they have seen, the host unveils a full-size machine, nearing completion. At a similar gathering one week later...