In ""Tarzan the Invincible,"" Tarzan's monkey friend Nkima stumbles upon a sinister plot unfolding in the jungle and rushes to alert Tarzan. They uncover a group of communists intent on raiding the lost city of Opar for its gold. Meanwhile, Queen La, the city's ruler and high priestess, has been stripped of her power and is being held captive by her own people.
As Tarzan confronts these challenges, he is determined to restore order to Opar. The backdrop of the rising Communist threat adds intrigue, though it serves primarily as context rather than a focal point. The story delivers a classic Tarzan adventure, filled with relentless action and excitement typical of Burroughs's work. Readers can expect thrilling encounters with lions and leopards, fierce hand-to-hand combat, daring prison breaks, and more. Ultimately, this novel showcases Tarzan's unwavering bravery and resourcefulness as he battles to reclaim Opar and rescue its queen.