In WWII Netherlands, resistance-leader Arie is killed by Dutch SS-man Niels, leaving his comrades, who pledge to avenge him. 35 years later, one of them, Ab, confronted with Niels again, decides to round up his old friends to kill him but they're no longer as devoted. Only former communist Gerben has stuck by his pledge and joins the execution.

Sherlock Jones is a handyman, a nice man who dreams of doing great things. Together with his dog Watson, he becomes involved in the case of the Karthoum diamond. This legendary stone arrives in the Netherlands to be cut and polished. The mafia attempts to steal the diamond during its transport from Schiphol Airport. They ensure that all security measures are checked by the 'renowned' private detective, because they know he will have no idea what is going on. The robbery is a great success. It's a good thing Watson is there too...