One of the weirder moments of Part 3 of Twin Peaks: The Return (and that's really saying something) happened when Dougie Jones (Kyle MacLachlan), the decoy Agent Cooper's (Kyle MacLachlan) evil doppelgänger (also Kyle MacLachlan) created to send to the Black Lodge in his stead, arrived at the Lodge.
"I feel funny," Dougie said to MIKE (Al Strobel). "What's happening to me?" Then his left hand started shrinking and the green ring on his ring finger slid off. His head turned into smoke and his body disintegrated and all that was left was a gold pearl.
I'm not going to touch what the significance of the pearl is supposed to be for now, but the green ring is an important, if inscrutable item in Twin Peaks mythology that has appeared many times, causing numbness in its wearer's left arm every time.
The ring has no official name, but is often called the Owl Cave ring after the symbol engraved on its stone. Owl Cave is located in the woods outside Twin Peaks and is covered in Native American petroglyphs, including this one. Taken together, the glyphs explain how to enter the Black Lodge.
The exact link between the ring and the cave is unclear, but whatever it is, it goes back very, very far. As explained in Twin Peaks' co-creator Mark Frost's tie-in novel The Secret History of Twin Peaks, the first recorded occurrence of the ring happened before Caucasian people ever arrived in what is now Twin Peaks, when a mysterious tribe of white indigenous people who lived near the waterfall gave the ring to the Nez Perce tribe. Chief Twisted Hair carried it with him in a leather pouch, but knew it should never be worn. He gave the ring as a gift to the explorer Meriwether Lewis, as in Lewis and Clark, who may have been driven insane by the ring. He had a psychedelic vision while wearing the ring near the waterfall and was never the same after. He had the ring with him when he died under mysterious circumstances a few years later. The ring was stolen by Major James Neely, Lewis' traveling companion at the time of his death, who may have passed it to the traitorous American statesman James Wilkinson, a political rival of Lewis'.
In later years, the ring was spotted in the possession of rocket scientist/occultist Jack Parsons, who died in an explosion that completely destroyed his right arm and who some say may have summoned a "fire demon" that killed him. President Richard Nixon wore it in the late '60s. Later it belonged to Air Force Major Dougie Milford, who spent his career investigating UFOs and supernatural occurrences before retiring home to Twin Peaks. His name may or may not be related to Dougie Jones.
After that, it somehow passed into the possession of Teresa Banks (Pamela Gidley), who was murdered by BOB (Frank Silva) the year before Laura Palmer (Sheryl Lee) in nearby Deer Meadow, as seen in Fire Walk With Me. Banks lived in the Fat Trout Trailer Park near Mrs. Chalfont/Tremond (Frances Bay) and her grandson, who are Black Lodge beings with an unclear, but definite connection to the ring and the rest of the garmonbozia gang.
When Agent Chester Desmond (Chris Isaak) was investigating Banks' murder, he looked underneath her trailer and saw the ring on top of a mound of dirt. When he reached for it, the picture froze. Desmond was never seen or heard from again.
Annie Blackburn (Heather Graham) wore the ring when she came back from the Black Lodge in the original series finale, but it was stolen from her finger by nurse as she recovered in the hospital. The Annie plot seems to have hit a dead end, though.
When Agent Phillip Jeffries (David Bowie) was telling the FBI about infiltrating the room above the convenience store in Fire Walk With Me, The Man from Another Place (Michael J. Anderson) said "with this ring I thee wed." It seems like a non sequitur, but he might actually be explaining the ring's power and letting on that the ring is made from a chip off the room's green formica table. In Laura's dream/vision of/visit to the Black Lodge, he showed the ring to Cooper, who warned Laura not to take it. She did take it, perhaps unwillingly, when Annie appeared to her in a vision, but the ring disappeared from her hand while she held it.
Later in the movie it reappeared on MIKE's hand when he confronted Leland (Ray Wise)/BOB about stealing his garmonbozia (that is, the pain and sorrow on which Black Lodge demons feed), which was the moment Laura learned for sure that BOB and her father were the same. When BOB was trying to possess Laura in the train car, MIKE threw the ring inside. Laura put it on, which prevented BOB from possessing her, so he killed her instead.
The prevailing theory about this is that by putting on the ring, Laura "married" MIKE and his arm, the Man from Another Place, which protected her from BOB, MIKE's former partner. MIKE became the owner of Laura's garmonbozia, just like he was the rightful owner of Teresa Banks', though BOB stole Teresa's. There's a theory that the ring makes its wearer's left arm go numb because that's the arm MIKE cut off himself.
It's hard to say if the ring is good or bad. It protects, but it also condemns. BOB may not be able to possess the wearer, but he still kills them. It seems like the ring drew Cooper to Dougie instead of the doppelgänger. Its clearest purpose seems to be to claim souls for the Black Lodge, but it's possible that the ring does whatever Mark Frost and David Lynch need it to do.
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