A young man happens upon a strange, isolated village which is oppressively ruled by foreign soldiers. When he tries to inquire into what is going on, he is forced to flee to an island where a renegade medical doctor tries to force him into submission.

Swiss allotment gardener Livius is murdered in his garden on French soil. The case must therefore be investigated by both the Swiss and French police. This leads to friction between the two forces. To make matters worse, Hunkeler has to cut short his vacation.