"It looked like one-third of a circular object. You put the three parts together, it makes a key and it opens... something."―Indiana Jones[src]
The Key to the Tomb of the Gods was an artifact that could be used to open the Tomb of the Gods. Its origins may predate paleolithic human cultures. The key had carvings that formed a map of where the Tomb of the Gods could be located. Part of the map showed the northern coast of Siberia.
In 1931, Henrik Mellberg, Francis Beresford-Hope, and Marwell O'Brien sought the key and discovered it in a diamond mine at the Popigai Crater, north of Norilsk, Siberia. Forming an expedition, they followed the map and reached the Tomb of the Gods, where the rest of their party died, and the three may have lost their sanity. Returning to civilization, they divided the key into three sections to protect the secrets of the Tomb of the Gods from falling into the wrong hands. The men then moved to different parts of the world, but kept in touch.
In 1936, fearing that O'Brien's piece had been lost to the Ahnenerbe, Mellberg contacted Indiana Jones to have him continue the quest of safeguarding the key. However, Friedrich von Hassell and his agents were on Mellberg's trail and shot the archaeologist in New York City. Jones was able to take Mellberg's piece of the key, and learn that Beresford-Hope was supposed to be in Tibet. However, in his escape from the Ahnenerbe agents, the piece was stolen at gunpoint by Janice Le Roi, in disguise.
Jones and Marcus Brody traveled to Tibet to find Beresford-Hope's piece of the key before the Nazis could obtain it. They met Alex Beresford-Hope, who allied himself with them, and showed them his father's piece, which had a carving which resembled the northern coast of Siberia, indicating that the pieces were also a map. Jones and Beresford-Hope set off by freighter to the north, from Shanghai, but after a stop in Japan, Beresford-Hope and his piece were captured by von Hassell. Le Roi, now working for the Nazis, was then betrayed by von Hassell, who took her piece and cast her and Jones adrift. Having already acquired O'Brien's piece, von Hassell now had all three pieces, which would lead him to what the key opened.
While von Hassell had the key, Jones and Le Roi had made copies of the map shown on their respective pieces, and once the map fragments were combined, they were able to catch up to von Hassell in northern Siberia.
Reaching the underground Tomb of the Gods, von Hassell tried to force Beresford-Hope into using the key to open the main doors of the giant vault. When Beresford-Hope refused, von Hassell killed him. While several of von Hassell's agents were possessed by the Tomb and opened fire on the rest of the party, von Hassell took the key and placed it in the inset in the doors, causing them to rumble open. WIth the doorway opened, von Hassell continued inside, leaving the key behind. The key was likely lost when Indiana Jones dynamited the tomb, causing it to collapse.