Sign of the Green Arrow: A Mystery Story

In Short

The story follows a young man named Johnny Thompson, who signs on as a deckhand for an oceanographic expedition led by a professor and his adventurous companions, Dave and Doris. Using a specialized "steel ball" for deep-sea exploration, the team captures rare marine life and photographs the ocean floor. However, their scientific mission is interrupted by the presence of mysterious foreign spies and the plight of a local family. Through persistence, courage, and technological ingenuity, the team uncovers a web of espionage, rescues a trapped submarine crew, and finds their own purpose.

The Story

The Sea Nymph anchors in calm, phosphorescent tropical waters, where Johnny Thompson keeps watch. While the rest of the crew sleeps, he observes suspicious lights flashing in a pattern on the distant hills—an "arrow" of green lights that serves as a signal. Johnny soon joins the professor and Dave in the Sea Nymph’s steel diving bell, a marvel of engineering that allows them to descend into the "eternal night" of the deep sea to film life forms previously unseen by man.

As they explore, they encounter a massive, sea-green octopus and realize that their presence is being monitored by hostile forces. These are not merely local inhabitants, but international agents operating from a hidden, castle-like prison on the island. The spies are using the islands as a staging ground for potential air raids against the United States, a threat that weighs heavily on an elderly, protective local man named Mr. Kennedy.

The tension rises when a submarine, manned by young, misguided foreign agents, becomes trapped on the ocean floor. Among those aboard is Mildred, Kennedy’s granddaughter, who had been swept into the conflict. Through their specialized diving equipment and wireless communication, Dave and the research team coordinate with the U.S. Navy to facilitate a rescue. Johnny, meanwhile, proves his mettle by tracking the spies’ movements through the jungle and uncovering their hidden cache.

The resolution comes when the trapped submarine is raised to the surface. Rather than meeting a violent end, the youthful crew is apprehended by the navy, and the crisis is averted. With the spy ring dismantled and the island’s safety restored, the research team prepares to return to the United States. However, Johnny decides to remain behind for a time to help Mildred and her grandfather recover their sunken family schooner. The story ends on a note of transition: Johnny looks forward to a future that includes college, while Dave promises that if they return to these waters, they will finally search for the legendary treasure that first drew them to the reef.

How It Unfolds

The voyage begins Johnny joins the Sea Nymph as a lookout, initially expecting a routine scientific trip. He quickly discovers that the tropical night hides more than stars, as he witnesses mysterious, coded lights flashing from the island shore.

Descending into the abyss The narrative shifts to the deep sea, where the characters use a pressurized steel ball to reach the ocean floor. They encounter strange, terrifying creatures and capture footage that thrills the professor, all while sensing that they are being watched from above.

The shadow of spies Johnny becomes convinced that "European spies" are operating in the region, using the islands for military positioning. He and the islander Samatan navigate the jungle, uncovering evidence of a covert operation that threatens the peace of the local community.

The rescue mission A submarine becomes stranded on the sea bottom, placing the granddaughter of a local resident in mortal danger. The Sea Nymph crew uses their diving bell to reach the site, coordinating a desperate rescue that brings the clandestine conflict to a head.

The final discovery The submarine is successfully raised, and the spy threat is neutralized by the arrival of the naval authorities. The team celebrates their victory, and Johnny chooses to stay on the island, signaling his growth from a mere deckhand to an independent man ready for his next chapter.

The People

Johnny Thompson starts as a restless, eager youth seeking adventure. He possesses a sharp eye for detail and a knack for photography, which he uses to document the spies’ activities. By the end, he has matured into a decisive leader who chooses to commit himself to the island's future.

Dave is the technical lead and the pilot of the steel ball. He is driven by a passion for discovery and an unshakeable faith in his equipment. He remains cool under pressure, whether facing a giant octopus or negotiating with a trapped submarine.

Doris serves as the vital link between the explorers in the deep and the crew on the surface. She is observant and brave, often acting as the voice of reason when the others are consumed by the thrill of the hunt or the danger of the situation.

Mr. Kennedy is an aging, vigilant protector of his home. He views the islands as a strategic frontier and is deeply suspicious of foreign influence. His fierce love for his granddaughter, Mildred, drives much of the emotional stakes of the final act.

Samatan is the native guide and crew member who bridges the gap between the researchers and the island. He is a man of the sea and jungle, possessing a wisdom that Johnny comes to respect deeply.

In Its Own Voice

"You must go up or down! Up into the stratosphere--or down, into the sea."

The professor explains his philosophy of exploration to Johnny, identifying the deep ocean as humanity's final, unexplored frontier.

"There's a place up there built of stone, half castle--half prison," Kennedy said, thoughtfully.

Kennedy warns Johnny about the dangerous, abandoned structure that serves as a signal tower for the spies.

"These, alone, will add greatly to the world's riches," he said, placing a trembling hand on Johnny's shoulder.

The professor recognizes the immense scientific value of the photographs Johnny has captured from the bottom of the sea.

What It's Really About

The book explores the tension between the innocence of scientific discovery and the harsh reality of global geopolitics. The "last frontier" of the deep sea is framed as a place of wonder, yet it is inextricably linked to the surface world's conflicts. The story argues that knowledge—whether it is the ability to photograph the dark corners of the ocean or the capacity to decode a secret signal—is a form of power. Ultimately, it emphasizes the importance of taking responsibility for one's environment and protecting the "simple" or vulnerable people from those who would exploit them for territorial gain.

Why Read It Today

This book will appeal to those who enjoy classic, fast-paced "boys' own" adventures where technology and pluck overcome impossible odds. Reading it feels like stepping into a time capsule; the prose is direct and energetic, reflecting the optimism and curiosity of 1930s pulp literature.

Readers should be prepared for the period-specific attitudes embedded in the text. The depiction of the local native population, while often sympathetic, reflects the paternalistic viewpoints common to mid-century adventure fiction. Furthermore, the book’s geopolitical anxieties—focusing on "European spies" and the vulnerability of the Caribbean—are direct products of its 1939 publication date, providing a fascinating, if dated, window into the anxieties of that era.

What lingers after the final page is the sense of wonder associated with early deep-sea exploration. The descriptions of the steel ball and the terrifying, beautiful creatures of the abyss remain the most vivid elements. While the plot moves quickly and relies on the tropes of its time, the underlying themes of courage and the desire to protect one’s home give the story a warmth that transcends its age. It is a brisk, light read, perfect for someone interested in the history of juvenile fiction or simply looking for a nostalgic, seafaring mystery.