In the preceding book, The Secret of the Unicorn, Tintin and Captain Haddock discover three parchments detailing the whereabouts of The Unicorn, a 17th century naval ship commanded by Haddock's ancestor Sir Francis Haddock. The Unicorn was scuttled by Sir Francis while fighting the pirate Red Rackham. Tintin and Haddock have confidence that the pirate captain's treasure is in the remnants of the sunken ship.Both Tintin and Haddock hire a fishing trawler, the Sirius, in order to hunt for the treasure. As the ship’s crew prepare for the search, their plans are discovered and publicized by the press, forcing Tintin and Haddock to deal with a plentiful amount of strangers claiming to be Rackham's descendants, insisting on a portion of the treasure. They are swiftly repelled by Haddock, who reminds them he is the descendant of the man who killed Red Rackham.Another petitioner is Professor Calculus, an unusual and hard-of-hearing inventor who offers the use of a special shark-shaped, electrically powered one-man submarine to aid in the search for the sunken ship without being disturbed by the abundant number of sharks in the region. The treasure hunters turn his offer down and prepare to embark for the Caribbean.Before Tintin and the Captain leave the port, the two detectives Thomson and Thompson join the crew in order to protect their friends from the possible threat of the rival, criminal treasure hunters, The Bird Brothers. Not long after leaving, Tintin and Haddock discover that Calculus has stowed away inside a lifeboat on board the Sirius. The professor has stored the unassembled parts of his submarine in the hold, removing the Captain's crates of whiskey in the process. Even though initially threatening to throw Calculus into the hold on bread and water, Haddock grudgingly decides to keep him along for the trip and gives him a cabin.The expedition reach the location stated in Sir Francis’ parchments. To begin with, the party cannot find anything at the coordinates (20|37|42|N|70|52|15|W|, off the Mouchoir Bank), but then Tintin theorises that Sir Francis used the Paris Meridian instead of Greenwich Meridian (which would yield 20|37|42|N|68|32|1|W|, off the Navidad Bank). Upon reaching the latter location, the ship comes across an unknown and uninhabited island. As they come aground to reconnoitre it, Haddock stubs his toe on a piece of wood sticking out of the sand, which upon excavation turns out to be the remains of Sir Francis Haddock's jolly boat. As they travel further into the centre of the island, they discover numerous skulls, which Tintin presumes are the remains of the island's cannibalistic former residents. There is also a splendid pagan icon of Sir Francis, and numerous parrots that repeat the Haddockian slang, which amuses Tintin, realizing that it has been passed down from generation to generation.Calculus's Shark-proof submarine proves very useful in searching for the remains of the Unicorn, while the actual inspection of the wreck itself is performed with a hardhat diving suit. Thomson and Thompson soon start to regret their decision to join the treasure hunt, because they are entrusted to manning the air pumps supplying the diving suit with oxygen when Tintin, and later Haddock, explore the wreck. While facing difficulties like shark attacks, they discover a cutlass, a gold bejewelled cross, a coffer of old documents, the figurehead of the ship and, to Captain Haddock's elation, a large supply of vintage Jamaican rum.While the search is otherwise ineffective, the crew spots a large wooden cross on the island itself which Tintin believes is the reference in Sir Francis' parchments to "the Eagle's cross" and could refer to it as the marker for the treasure's location. Upon coming to the cross the party begins to dig, but after not too long Tintin realizes that they are following a false lead, considering that Sir Francis would not deliberately leave his treasure on an island he did not intend to return to, so they return to the ship. Time passes. Although there are additional dives to the wreck, they are unable to find the treasure itself and they go home disappointed.Calculus examines the documents from the retrieved strongbox, which allows him to determine that Sir Francis was the owner of the large estate of Marlinspike Hall, the former residence of the Bird brothers. Upon this revelation, Tintin insists that Haddock should purchase the estate, which is up for auction, but the Captain is short on money due to the large expense of their unsuccessful treasure hunt. However, Calculus, who had received a large undisclosed sum of money from the government after a lucrative sale of his submarine design, lends Haddock the money for the property.After purchasing Marlinspike, Tintin and Haddock explore the cellars of the main house. Amongst the Bird Brothers' cluttered antique collection they find a statue of Saint John holding a cross. Tintin abruptly cries out, "The Eagle's cross!" as he remembers Saint John is entitled "The Eagle of Patmos". At the statue's feet is a globe. On it, Tintin locates the island where Sir Francis Haddock was marooned is depicted. He touches that point and ascertains it to be a trigger button—the globe springs opens and Red Rackham's treasure is found concealed inside it.
Later on, the Captain and Tintin open a museum in the maritime gallery of Marlinspike Hall dedicated to Sir Francis Haddock and the antiques found on the expedition.
- The comic book continued the story that began in "The Secret of the Unicorn", involving the search of Red Rackham's treasure.
- The comic book introduced the character of Cuthbert Calculus, who become a pivotal character in subsequent comic books.
- Captain Chester, who appeared in "The Shooting Star" and was mentioned in "The Secret of the Unicorn", was mentioned again in this comic book. He was subsequently mentioned again in "The Seven Crystal Balls" and in "The Castafiore Emerald".
- An early version of The Sirius previously appeared in "The Shooting Star".
- Ivan Ivanovitch Sakharine, a pivotal character of "The Secret of the Unicorn", made a cameo appearance at the end of this comic book. He later returned in a cameo appearance in the unfinished "Tintin and Alph-Art".
- Max Bird, one of the Bird brothers of "The Secret of the Unicorn", was mentioned in this comic book. He was supposed to return along his brother Gustav Bird in the unfinished "Tintin and Alph-Art", but they never returned due Hergé's death.
- Captain Haddock
- Cuthbert Calculus
- Thompson and Thomson
- Ken Rogers
- Ivan Ivanovitch Sakharine
- Aristides Silk
- Sir Francis Haddock (mentioned)
- Red Rackham (mentioned)
- Max Bird (mentioned)
|The Adventures of Tintin|