The demented archaeologist Dr. Andrew Forbes (George Zucco) discovers a living, breathing serpent creature known to the Aztecs as Quetzalcoatl (the Killer Bird God) and accidentally kills his wife by giving her one of the beast’s feathers, causing the creature to track her down and slaughter her. Now Dr. Forbes uses this twisted knowledge to extract revenge upon his enemies by placing one of the serpent’s feathers on his intended victim and letting the beast loose to wreak havoc.
The movie begins with title and credits shown over Aztec stone work. A scroll contains a foreword, "Near the little city of San Juan, New Mexico, stand the Aztec ruins. Archeologists tell us they are the remains of a once great temple, abandoned by the Aztecs when they migrated south to the Valley of Mexico, where they founded a rich empire. To defeat the greed of Cortez and his Spanish adventurers who had inaugurated a campaign of loot and murder, the wiley Emperor Montezuma hid his fabulous treasure far to the north and implored his native gods to guard it. Among these gods was the feathered serpent—Quetzalcoatl." We see the creature in its lair. A car passes by the ruins and Professor Andrew Forbes (George Zucco) is driving. He walks to an opening in the mountain. He walks through an underground chamber lit by torches. He paws a handful of gold and jewels in a treasure chest. The hiss of his captive creature draws his attention to a niche covered with bars. He talks to his pet, "More than 300 years, Quetzalcoatl, you have guarded the treasure of Montezuma. Now you protect it for Professor Andrew Forbes. As I have found it five years ago, it's mine by right of discovery. No other human eye shall see it and live." He pulls a feather off the creature, and taunts it. He knows it will kill to get it back.Dr. John Lambert (James Metcalf) reviews his most recent article, "Aztec Carving of the Legendary Bird Quetzalcoatl." Mary Forbes (Hope Kramer), step daughter of Professor Andrew Forbes, has stopped by to see Lambert. She warns Lambert that her father will be upset about the mention of Montezuma's treasure legend. She also mentions that her father has been acting strangely and disappears for long periods. Forbes bursts into the room and demands words with Lambert. Forbes pulls a feather from his pocket and drops it to the floor, and then storms out. Mary looks down and finds the feather. Lambert immediately recognizes the feather and tells Mary it is very rare. He explains that the creature was half bird and half reptile and that it lived on blood. The three other feathers, known to exist, were found on dead men whose throats had been torn open. Mary goes home and talks to her father about the feather. Forbes excuses himself and drives back to the mountain lair. Lambert has an appointment with a man named Hastings in the nearby town of Azteca. Pulling a lever, Forbes releases Quetzalcoatl from his cage. It flies off seeking its feather. Lambert stops his car and gets out. He hears the growls of the flying creature and pulls the feather out of his coat pocket to compare it to the flying creature he sees. Too late he realizes it is flying straight toward him. He dives into some bushes, but the creature lands on him and kills him. It flies back to the mountain entrance of its cage and is secured by a gloating Forbes. Newspaper headlines report on the death of Dr. John Lambert.In New York City and the studio of XOR radio, an announcer (an uncredited Richard Crane) tells his audience that Richard Thorpe (Ralph Lewis) will be doing an exclusive coverage of the case in detail. He will fly out to New Mexico and do his daily broadcasts live and will solve the case. Forbes and Mary sit and listen to the broadcast on the radio. The news manager, Mr. Grant (uncredited) is not amused by the whole scheme. Mary informs her father that Thorpe is very clever and only requires one tiny clue to solve cases.Forbes returns to the lair and retrieves another feather from Quetzalcoatl and says to himself, "Here's your clue, Mr. Thorpe." At the San Juan County Jail, Sheriff Bill Hayes (Henry Hall) meets with Thorpe, Jerry Jones (Eddie Acuff), the radio technician, and Professor Louis Havener (Wheaton Chambers), an ornithologist. Hayes sarcastically asks Thorpe, "Are you going to solve the murders today, or are you going to take a couple of days?" They part with an understanding that nothing will be done to jeopardize the investigation or the criminal case. Dr. Wagner (uncredited) provides details of the death of Lambert to the radio audience and to the Head of the Inquest (Budd Buster). The most startling fact is that the body was drained of blood. Hayes testifies that there were no footprints near the body. Forbes testifies that he and his step daughter saw him earlier in the day. He confirms the mythical creature was called Quetzalcoatl and that he has been doing archeological work. Thorpe asks Forbes about the death of his late wife under similar circumstances. Mary provides testimony about the feather. Next is Hastings (Milton Kibbee). He confirms that Lambert had shown him the feather, but he had not dropped it off at the Lambert home. Havener completed the days testimony with information about Quetzalcoatl. The jury of the coroner's inquest determines that Lambert's death was a homicide. Forbes agrees to help Thorpe with his investigation and offers to drive him out to the site of the murder. Once there, Forbes plants another feather and then leaves Thorpe to find it. Sheriff Hayes drives up and talks to Thorpe. Hayes spots the feather where Forbes planted it. He wants Hastings to see and identify it. Hayes tells Thorpe to drive to Azteca and bring Hastings back. Hayes picks the feather up in his hands. Forbes releases Quetzalcoatl to kill Thorpe, but Hayes is killed instead. Thorpe and Hastings return in time to see the creature fly off and find the Sheriff's body. The creature returns to its cage.Thorpe calls Forbes and asks to speak to Mary. Forbes takes a message, but tells his step daughter to stay away from Thorpe and Pine Mountain. Thorpe and Havener find the feather as Forbes pulls up in his car. They leave for the radio station in Pine Mountain. Havener examines the feather. Thorpe exits the waiting room to do his broadcast. He reports that Sheriff Hayes was killed and that he saw the prehistoric creature with a long reptilian tail. He intimates a man is involved, but does not reveal the name. Quetzalcoatl flies into the window at the radio station and kills Havener. Mary's screams bring Thorpe into the waiting room where he fires a gun at the departing creature.Thorpe does his next broadcast in front of the Sheriff's office. One man, Vance Bennett (Terry Frost) claims he has an old Aztec treasure map and a device he calls a doodlebug that can locate gold. Forbes is intrigued and annoyed by this man. Thorpe invites Forbes over to meet Bennett. Forbes volunteers to assist Bennett in his treasure hunt. Grant has shown little interest in the case, but the added bonus of treasure now has piqued his interest. Bennett gives Thorpe a feather he obtained from a collector in Honduras. Thorpe intends to use the feather as bait and that Forbes is responsible for the deaths and the treasure. Forbes and Bennett search the area of the deaths with the device. Bennett pulls out the feather and plants it, then finds it and shows Forbes he has it and puts it in his pocket. Thorpe is hiding in a cave with a metal cage door on it. He steps out when Forbes excuses himself. Bennett steps into the cave and replaces the metal grating over the entrance. Thorpe goes after Forbes. Using binoculars he sees Forbes enter through the cave door. Forbes releases Quetzalcoatl which heads for Bennett. Jones manages to fall in front of the cave entrance. Bennett pulls him inside before the creature attacks. Bennett gives Quetzalcoatl his feather and the creature departs. Thorpe sees the creature return. Forbes closes the cage and takes one more feather. He intends to use it on Thorpe.At his home, Forbes is upset to see Mary stroking a feather. He demands to know where she got it. Mary tells her step father it was in his bedroom. Forbes lies and tells her he found it yesterday out at the ruins. Mary warns her step father that he may be associated with the murders. Mary makes the connection between the feather and the death of her mother. Forbes takes Mary out to see the treasure and the creature. Thorpe does his next broadcast from inside the mountain lair of Quetzalcoatl. He mentions the creature, the method of murder and that he will soon unmask the killer. Something goes wrong with the equipment and the transmission goes silent. Forbes and Mary drive out to the ruins. Forbes shows her the entrance and warns her of how dark it is. Thorpe is now outside with Jones working on the equipment. Forbes opens the treasure chest. Jones has fixed the transmitter and they hear Forbes and Mary talk about the treasure. Forbes tells Mary, "It's mine, mine do you hear, all mine. I'm the richest man in the world." Thorpe runs to save Mary as Forbes escorts Mary over to the cage. She accuses Forbes, "Then you did kill Dr. Lambert and all the others." Forbes pulls another feather off Quetzalcoatl just as Thorpe runs in. The two struggle and the cage door is opened. Forbes, still holding the feather, runs out of the mountain chamber. Quetzalcoatl flies directly for its feather and the thief who stole it. It attacks and kills Forbes. Thorpe takes a couple of shots at the creature and brings it down. Thorpe finishes his broadcast with the announcement of his engagement to Mary. We close with Grant punching the announcer, telling him, "That was for not phoning Thorpe to cut me in on that treasure."