After spending some time with his diplomat father in Germany, a young French medical student returns by train to Paris to resume his studies. He is puzzled by the harsh treatment he receives from customs at the border but doesn't begin to understand why until he gets home and discovers a mummified head in his luggage. He suspects that someone at customs put it there, but is not sure. Instead of reporting the meandering body part, he decides to investigate it using the tools he has as a medical student. It appears to be the head of a Russian who died somewhere in Asia.