Super Thriller Comic #12 (1948)

Ace Hart ventures into the jungle of Zantal to investigate the disappearance of Professor Hughes and his expedition, following rumors of strange horned creatures. After encountering a terrified survivor and a monstrous ape, he learns the explorers were attacked by mysterious, fire-wielding beings known as Devil Soldiers—creatures whose origins remain unknown. With the professor and his daughter now in danger, Ace prepares to face the Devil Soldiers head-on as they close in on Death Valley.

In the isolated depths of a forgotten island, two shipwreck survivors, Bob and Jack, stumble upon a hidden cave and are captured by a reclusive professor who claims to be their host—though his "welcome" comes with armed guards and a sinister air. As the professor reveals his secret laboratory and a fleet of advanced aircraft, the boys realize they’ve fallen into the hands of a madman with plans to dominate the world, forcing them to outwit his traps and find a way to stop him before it’s too late.

Jack and Peter Strong, exploring a South American river, stumble upon a river flowing uphill and a hidden tunnel leading to the Secret City of the Marva—a civilization centuries ahead of their time. Taken prisoner and imprisoned as part of a sinister experiment, they team up with Jasmine, a young woman whose father was killed by the Marva, to escape the underground city and find their way back to the surface.