Red Rackham's Treasure (French: Le Trésor de Rackham le Rouge) is the twelfth of The Adventures of Tintin, a series of classic comic-strip albums written and illustrated by Belgian writer and illustrator Hergé, featuring young reporter Tintin as a hero. It is a continuation of The Secret of the Unicorn, and is one of very few Tintin books to directly carry on the story of the preceding title. It is notable for the first appearance of the eccentric and deaf but ingenious Professor Cuthbert Calculus. According to Michael Farr's Tintin: The Complete Companion, it is also the best-selling book in the Tintin series.
In The Secret of the Unicorn, Tintin and Captain Haddock discovered the location of the Unicorn, a pirate ship which was blown up in the West Indies by Captain Haddock's ancestor Sir Francis Haddock in 1676. After destroying the vessel, Sir Francis fled to a nearby island. Tintin and Captain Haddock believe that the eponymous pirate's treasure, taken by Sir Francis, remains hidden on that island. Red Rackham's Treasure depicts their search for the treasure.
Tintin and the Captain hire the Sirius, a boat under Haddock's command, to search for said treasure. As the crew prepare for the search, their plans are discovered and publicized by the press, forcing Tintin and Haddock to deal with numerous strangers claiming to be Rackham's descendants and insisting on a share of the treasure. They are quickly driven away by Haddock, whose claim to be the descendant of the man who killed Red Rackham has more weight.
Another petitioner is Professor Cuthbert Calculus, an eccentric and largely deaf inventor who offers the use of a special shark-shaped, electrically powered one-man submarine to help search for the sunken ship without being bothered by the numerous sharks in the area. The treasure hunters turn him down and later set off for the trip.
Before Tintin and the Captain clear the port, their friends, Thomson and Thompson intercept them with orders to join the crew to protect the treasure hunters from the possible threat of Max Bird, a rival treasure hunter who escaped from prison. (Ultimately, Bird is never seen or mentioned again, making him a MacGuffin for getting the detectives on board the ship). Shortly after the departure, Tintin and Haddock discover that Calculus has stowed away on board (in a lifeboat, complete with bedclothes;pillow and blanket stolen from the Thompson twins cabin over which they are shown quarreling; and a tin of biscuits which the ship's cook had blamed Snowy for swiping from the galley). The professor has stashed the unassembled parts of his submarine in the hold--removing the Captain's crates of whisky in the process. Despite initially threatening to throw Calculus into the hold on bread and water, Haddock grudgingly decides to keep him along for the trip.
Although it is never directly stated in the book, the coordinates given in the parchment place the island in the Caribbean, to the north of Hispaniola. Initially, the party cannot find anything at the coordinates but then Tintin hypothesizes that Sir Francis Haddock used a Paris meridian instead of the Greenwich one (which would yield ). Sure enough, the ship reaches an unknown and uninhabited island, where Tintin and his friends believe the treasure to be buried. As they come ashore to explore it, the Captain stubs his toe on a piece of wood protruding from the sand, which is excavated and turns out to be the remains of Sir Francis Haddock's rowboat. As they penetrate into the interior of the island, they encounter numerous skulls, which Tintin deduces are the remains of the island's cannibalistic former inhabitants. There is also a magnificent pagan icon of Sir Francis, and numerous parrots that repeat the Haddockian argot, which an amused Tintin realizes has been passed down for generations.
Calculus's submarine proves useful in searching for the sunken Unicorn, while the actual examination of the wreck itself is performed with a hardhat diving suit. The Thompson twins soon begin to rue their decision to join the treasure-hunt, because they are consigned to manning the gigantic air pumps supplying the diving suit when Tintin, and later the Captain, explore the wreck. While facing complications like shark attacks, they discover a gold bejeweled cross, a strongbox of old documents, the figurehead of the ship and, to Captain Haddock's delight, a large supply of vintage Jamaican rum.
Although the search is otherwise unproductive, the crew spots a large wooden cross on the island itself and Tintin believes that the reference in their map to "under the Eagle's cross" could refer to it as the marker for the treasure's location in Sir Francis's calendar etchings. Upon coming to the cross the party begins to dig, but after a while, 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, and they return to the Sirius.
Time passes. Although there are further dives to the wreck, they are unable to find the treasure itself and they go home disappointed. Upon disembarking, the Captain is accosted by a reporter. In retribution for the unwanted attention brought earlier by the press to their expedition, Haddock impishly refers him to "my secretary, Mr. Calculus," whom the reporter tries to interview in vain.
Once home, Calculus's further examination of the parchment documents in the chest that they retrieved allows him to determine that Captain Haddock is heir to the large estate of Marlinspike Hall. Upon this discovery, Tintin insists that Haddock must purchase the estate (which is up for auction), but the Captain declines, noting that he is short on funds due to the wasted expense of their failed treasure hunt. However, Calculus, who has received large sums of money from the government after a profitable sale of his submarine design, overcomes that difficulty in gratitude for a successful test run.
After purchasing the Hall, Tintin and Captain Haddock explore the cellars of the main house. Amongst the cluttered antiques left by the malevolent Bird Brothers (the former owners), they find a statue of Saint John and Tintin remembers that he is called "The Eagle of Patmos" (the island where he was supposedly exiled to) and is often depicted with that bird. The statue is holding a globe, and Tintin finds the location of the island where Sir Francis Haddock was exiled. He accidentally discovers it to be a trigger button to open the globe. The treasure was hidden inside the globe — and the statue was holding a cross above it, just as the map indicated.