A serial killer named The Shark is terrorizing London by killing his victims with a speargun and then, dressed in a scruba-diver's wetsuit, using the city's sewer tunnels to make his getaway.

The young veterinarian Dr. Vlimmen settles in a small town on the North Sea coast. When he reports the conditions in the local slaughterhouse as cruelty to animals, he makes an enemy of the influential butcher van Heusden, who launches a smear campaign against him. Vlimmen is only supported by his sister Truus and his friend, lawyer Dacka, who loves Truus. In the end, Vlimmen succeeds in clearing his name. Through a daring operation, he regains his reputation and also finds Nel, the daughter of councillor van der Kalk.