The series is set in ancient Mexico, when the peaceful god Quala is being usurped by the new and vengeful god, Teshcata; a power struggle ensues between the just Emperor Kukulkan (Tony Steedman) and the scheming High Priest Nasca (Troughton). With the new temple built and riddled with secret passageways, Nasca plots his ascension through betrayal, cunning and murder. With the arrival of the rival Toltec army, led by Prince Heumac (Brian Deacon), the Emperor sees a chance for peace by arranging a marriage to his daughter, Chimalma (Diane Keen). This creates tension with the rival suitor Mahoutec, General of the Jaguar Guards (Robert Gray), whose jealousy becomes a tool which Nasca exploits to his deadly advantage. It takes the courage of Heumac's messenger boy, Tozo (Richard Willis) and his blind mentor, the prophetic Otolmi (George Cormack), to find a way to defeat the powers of darkness.
The first series focuses on Nasca's play for power, which leads to the Emperor's murder, the shaming of Mahoutec, the slaughter of the Toltecs and the imprisonment of Heumac. But at the time of the eclipse, the tables are turned on Nasca as he meets his fateful end. Or does he?
The second series follows on directly with Chimalma now preparing her reign with a new ally in court, Mataque (Robert Russell). Meanwhile, Heumac undertakes a series of tests of courage, wisdom and ingenuity to prove that he would make a worthy husband. But Nasca's followers are plotting, and Xipec, Governor of the Gold Region (Granville Saxton), uses the magic of witchwoman, Keelag (Shelia Burrell), to bring the High Priest back to life.
This show provides the following tropes:
- A God Am I: In the finale, Nasca goes from worshipping Teshcata to believing himself to be him.
- And I Must Scream: Part of Nasca's plan in the first series involves keeping Chimalma permanently in a state of drugged paralysis, so he can rule as regent. He tests the drug on Tozo and later Chimalma, but Huemac manages to give them the antitdote before Nasca can succeed.
- Back from the Dead: Nasca in the second series.
- Big Bad: Nasca.
- Big Good: Emperor Kukulkan. In the second series, his daughter Chimalma takes his place.
- Blind Seer: After the Aztecs began to worship Teshcata, Otolmi, the High Priest of Quala, was staked out in the desert with his face turned to the Sun until he was blinded. After he lost his sight, he gained the ability to see the future through prophetic dreams.
- Captain Ersatz: Quala, the titular Feathered Serpent, is one of Quetzalcoatl.
- Cold-Blooded Torture: Xipec has Tozo tortured for information.
- The Dragon: Nasca has two of them; Chadac in series one and Xipec in series two.
- Dreaming of Things to Come: Otolmi tells Tozo that he has foreseen Nasca's machinations in his dreams and visions and therefore knows that the life of Tozo's master Prince Heumac is in grave danger. He later forsees the defeat of Nasca and the Aztecs abandoning Teshcata in favor of their old god Quala.
- Human Sacrifice: Given the setting, this is a major theme. When Prince Heumac's delegation arrives from Tula, Nasca orders that ten people, including three volunteers, be sacrificed as a show of faith to Teshcata. As he is concerned about offending the sensibilities of Heumac and the other Toltecs, Emperor Kukulkan restricts the sacrifice to the three volunteers before calling it off altogether. After he manipulates Mahoutec into massacring the Toltecs, Nasca plans to sacrifice the 400 or so survivors so that the Aztecs' loyalty to Teshcata may be proven beyond all doubt. However, Chimalma, Heumac and Tozo manage to defeat his plans.
- Love Triangle: It had been long understood that Emperor Kukulkan's daughter Princess Chimalma would marry the greatest Aztec warrior Mahoutec, the leader of the Jaguar Knights, and that Mahoutec would one day succeed Kukulkan. Mahoutec is furious when he learns that Kukulkan plans to marry Chimalma off to Prince Heumac of the Toltecs so that they can return to the worship of the old god Quala and save their souls. Combined with Nasca's lies and subtle manipulation, this causes Mahoutec to try and kill Heumac so that he can have Chimalma for himself.
- Religion of Evil: The worship of Teshcata involves frequent human sacrifices as a sign of fidelity and encourages cruelty and brutality. Kukulkan and Chimalma, who long for the Aztecs to return to the peaceful religion of Quala, regard it as being evil and destructive to their way of life.
- Secret Path: Nasca had Maxtla include numerous secret passages in the newly built palace so that he could come and go as he is pleased and eavesdrop on conversations with impunity. After the palace is complete, Nasca has Chadac kill Maxtla so that he cannot reveal the truth to anyone else. However, before he dies, Maxtla manages to pass on a map of the secret passages to Tozo and Otolmi.
- The Speechless: Nasca's burly henchman Chadac is unable to speak and typically communicates with his master through gestures.
