A man realizes one day that a new conciousness, a stranger, has abruptly entered his mind. But this is not a voice in his head that tells him what to do; it asks nicely, with a German accent. After the initial shock, they grow to like one another and together they search for the reason of this anomaly. The only similarity that attaches them together is that they are both university professors in their respective cities, Miami and Regensburg. After transatlantic flights to France, where both had been vacationing, they succeed in finding out how it came to be that one consciousness came to squat inside the other, but this leads to complications with their respective mates as their lives quickly go out of control.