The novel is a continuation of the story in The Ship From Atlantis, telling of Prince Gwalchmai's star-crossed love for Princess Corenice of Atlantis in her various reincarnations, along with his centuries-delayed quest to secure aid and settlers to shore up the faltering empire established by his father and refugees from the fallen kingdom of Arthur in the New World. The story opens with Gwalchmai's reawakening after centuries in suspended animation. The Britain he finally reaches is a prostrated land transformed into England by its Saxon conquerors, with his father's exile long forgotten and his countrymen incapable of undertaking any sort of colonization project. Guided by his reincarnated lover, he seeks aid unsuccessfully, his travels taking him from Viking-age Europe to the far-eastern empires of the Chinese and Japanese, and ultimately back to Europe again as it approaches the Renaissance. He is abetted down through the centuries by the magical ring of his godfather Merlin, responsible for his longevity, and by Corenice. Highlights include the hero's visit to Faerie, his service as a companion to Joan of Arc, and his final revelation in Iceland of the secret of the New World to a Genoan merchant, Christopher Columbus.

The preceding books in the series, King of the World's Edge (1939) and The Ship from Atlantis (1967) were later reissued together by Ballantine as Merlin's Godson (1976), a title that has also been used for the series as a whole. Munn's research on Joan of Arc for Merlin's Ring sparked an interest that carried over into his epic poem The Banner of Joan (1975). In his last years Munn was reportedly working on a sequel to Merlin's Ring to be called The Sword of Merlin, which he did not live to finish.

• Merlin's Ring title listing at the Internet Speculative Fiction Database
• Zweig, Dani. "Belated Reviews PS#13: Misc 3: Historical Fantasy by Arnold/Munn/Moore"