John Héléna has escaped from prison, and now tries to get back golden bars hidden in the Discreet 's wrack. With a new mini submarine, Spirou decide to intercept him. Except that near the wreck, the sea now hides an even bigger secret, and "bubbles men" are trying to hide it. This story is followed by a short one, Les petits formats ("Small formats").
Tropes associated with this story include
- Underwater City: Korallion la bulle, the city that Mr d'Oups hide to the public.
