The Baron and his cronies steal a precious crown and hide in a secret room of an abandoned castle. With the help of their tiny robot Robin, Bassie and Adriaan set out to find the crown and return it to the museum.
Professor Archibald Chagrijn exposes the world to his blubbering gas, which makes people sad and causes them to cry. Bassie proves immune to the blubbering gas -- as he has had an overdose of laughing gas. The professor is hiding on the Canary Islands, but Bassie and Adriaan manage to track him down.
Bassie finds a treasure map in a painting he bought at a flea market. Three crooks are also after the treasure and try to take the map from our friends.
Bassie and Adriaan have a diamond named after them. Escaped from prison, diamond thieves B1 and B2 attempt to steal it, dressing as Bassie and Adriaan. The actual Bassie and Adriaan are given three days to prove their innocence.
Bassie and Adriaan take a well-earned holiday but find themselves chased by two diamond thieves, referred to as B1 and B2. The crooks mistake Bassie for the go-between who came to collect the key to the vault of the stolen diamonds.