Stefan, Hanno and Kalle are in the forest with Kostas to try out Kostas’s GPS equipment; he plans to "open up a whole new commercial opportunities" with it.
Geocaching is his new magic formula. However, even without any GPS equipment Kalle manages to find an unconscious man in the undergrowth as he is strolling around. Stefan discovers two small marks on his leg, close together, where something has punctured the skin: it looks like a snakebite. There are a number of empty plastic containers and boxes scattered nearby. They use Kostas’s pick-up to take the man to hospital. On the way they come across Pia and Olli in the police car, who go along with them.
Later they get a message from the hospital saying that the man with the snakebite, who claimed his name was Dahlke, didn't have any ID on him - and has now run off. But his life could be in danger, since he was bitten by a deadly monocled cobra.
Stefan takes the police officers back to the place in the forest where they found the man. But now the boxes and containers have gone. However, they spot some clear tyre tracks on the ground, and Stefan discovers a turtle in the bushes nearby.
They take the turtle to Kalle's vet, Dr Assmann, to find out more about it. But the lady vet on duty today, whose name is Schmook, doesn't seem to know much about exotic creatures.
Now Olli finds the man who ran away from hospital and discovers that his real name is Reuter. When questioned, the man confesses to Olli and Pia that he was to be paid €200 in cash for acting as a courier. He doesn't know the identity of the man who hired him. By now it is clear that Flensburg police are dealing with a case of animal smuggling. Naturally Stefan and the Flensburg Evening News mount an investigation at once and come up with a wonderful plan. They're going to use Reuter as bait, the next time he is asked to do a similar job. But when that time comes Reuter has to go into hospital because of complications with the snakebite. So Olli goes undercover to take the courier job instead.
With Kalle's help the police are able to arrest a supplier of exotic animals - but it turns out that this isn't the end of the case by any means.
Everything seems to revolve around animals back in the Andresen house, too. Merle is looking after a friend's rabbit, Hanno is collecting spiders and selling them as rare specimens from the Amazon delta, and Frau Jansen is trying desperately to escape from the Andresen children's scorpions.