Most of us don’t give any thought to ships sunk in the past, and if we do it at all it’s likely to be passing acknowledgement of a news report of a discovery or recovery. What The Treasure of the Black Swan lays bare is that locating a sunken ship is merely the first stage in a protracted and bitter political process.

The revelation takes a while from Guillermo Corral, who bases this on actual events, and as the cover sticker informs us, it’s a story that’s been filmed. We learn in the first twenty pages that an American marine research company named Ithica has successfully located something beneath the sea off the Spanish coast, and one of their first considerations is to retain a law firm. It’s through the experiences of rookie diplomat Álex Ventura that the story unfurls. He’s assigned to work at Spain’s Ministry of Culture, and meets Elsa in the Heritage Department who knows how Ithica lay claim to wrecks, how they circumvent the legal requirements of their exploration permits, and how requests for Coastguard intervention never come to anything.

It’s easy to see why what follows would appeal to dramatisers in both comics and film. Events unfurl almost cinematically including the possibility of romance, sinister visits from well informed people and a rip-roaring story of deceit and concealment over a fortune possibly worth billions in today’s money. It’s also a detective story in which the little guy is pitched against an enemy with limitless resources. It may seem strange that in this case the little guy represents the Spanish government, but there are combative and influential forces within it against which Ventura stands up. There are sections of courtroom drama, some early 19th century British piracy, and the chance meeting that would seem too coincidental if not real, and after a slow start The Treasure of the Black Swan positively zips along as the reader becomes embroiled in the intricacies.

Much of the success is down to Paco Roca’s disciplined and methodical artwork ensuring the clarity of complexity. He keeps the view restricted to several yards away from the focal point, and is excellent at distinguishing a large cast in order that we’re aware who they are when they change their suits. Roca also provides complete environments, whether they’re a government library or flight control tower, and importantly he can modify his style when necessary to add some variety when considering the past.

Like all good stories, just when everything appears resolved, previously hidden murkiness comes to light, and as Ventura was there at the beginning, he’s the person chosen to see everything through. It’s a far from simple task that keeps throwing up more problems, which test Ventura, but will thrill readers.

Unless you’re of the opinion that treasure seekers are automatically entitled to anything they find with no regard for cultural heritage, ownership when lost or territorial dominion, The Treasure of the Black Swan will be an engrossing adventure. If an action thriller provided by one of the top genre writers it would be spectacular, but that it’s real raises it a notch above. How real? We don’t know. Much is verifiable, and Corral’s previous career was diplomacy. Diplomatically he considers this a work of fiction based on events he witnessed. In the end it won’t matter. This is a great story.