A Most Annoying Island

A father tells his grumpy teen knave the story of Wolgergouw island, where a medieval witch hunt ended in the reeve and monk condemning to the drowning test of a woman, thus declared innocent. Se revealed being a white witch but now cursed the inhabitants to being excessively annoying until the conch she uses to impose the spell and drops into the lake is found and played by a pure soul. The curse remains confined to the island, until the Dutch government has a bridge built to link it to the mainland. The PM opens it and is instantly infected, turning into a diplomatic nightmare. The secret service has two biologists taken away from their simian observation project to be dropped on the island to find the problem, and hopefully a solution. That depends on cooperation with the only nice kid on the island and his class friend, a girl too recently arrived to be affected yet. But getting together isn't easy and meanwhile the army is ordered to seal off the bridge.