Major Characters:

• The Shadow/Lamont Cranston
• Barry Vinton: A millionaire big game hunter and sports fisherman.
• Joseph Hart: Vinton's friend and naval craft designer.
• Phil and Charlie: Former convicts who now work at Vinton's private shipyard.
• Mr. Brausch: Vinton's First Mate aboard the submarine.
• Captain Jones: Captain of a doomed ship.
• Mr. McClennan: Captain Jones's First Mate aboard the ship.

Featured Agents:

• Margo Lane

Minor Characters:

• Newspaper seller
• Frightened woman passenger
• Businessman
• Vinton's submarine crew
• Captain Jones's ship crew
• US Coast Guard
• Representative of Acme Steamship Agencies
• Representative of a shipping company
• Man addresssing the Maritime Commission

Synopsis: (Warning! Contains spoilers!)

We hear the ringing of a ship's bell. The first mate of the ship, Mr. McClennan, looks out over the sea. Something about it worries him. He expresses his concerns to Captain Jones, telling him that the waters have been calm and smooth for the last five days. A bad omen. The captain scoffs; it is nothing more than a sailor's superstitious mind playing tricks on him.

Suddenly, they hear an explosion from the engine room. The captain thinks it is more than a boiler that blew up. He calls down to the crew in the engine room. A sailor manages to answer him, and is about to tell the captain what happened when McClennan calls him (the captain) over. They see a path of white water heading straight for their ship. It is a torpedo! This shocks and puzzles the captain; there is no war going on, so why are they being attacked? He quickly tells McClennan to hold fast as the torpedo is about to hit...

As the ship sinks, the crew manages to climb aboard a lifeboat and lower themselves into the water. At that moment, they spot a submarine rising out of the sea. So this is the culprit who sent the torpedo at them. To the crew's horror, a man emerges from the submarine, wielding a machine gun. He opens fire on the helpless sailors.

The captain's pleas for mercy are drowned out by the bullets...

We now hear the newspaper seller announcing a headline about a massacre on the high seas. Acme Steamship Agencies receives a phonecall from a frightened woman wanting to cancel her reservation on their cruise ship, the Princess Marie, claiming that sailing would be suicide. Elsewhere, a shipping company tries to convince a businessman to ship their goods with them, and assures him that their ships are safe. The businessman does not believe them. When told that his goods will be insured, he retorts that the insurance rates will be four times higher than usual. He cancels his shipment.

The Maritime Commission now has a huge problem on its hands. For the last three months, 18 ships from around the world have been mysteriously sunk. In the panic that ensued, passengers have cancelled their reservations, freight shipments are being withdrawn, even crewmen have deserted their ships. No one wants to be on the high seas, and there is nothing the Maritime Commission can do.

At a restaurant somewhere, Lamont orders another round of coffee for himself and Margo. They discuss the mystery surrounding the sunken ships. Lamont notes that three months ago, the first ship disappears, then a few days later a second ship was sunk and the bullet-ridden bodies of its crew were found dead in their lifeboat. Each succeeding disaster has been increasingly gruesome. Lamont points out that international jealousy is not a cause, since each of the ships were from a different country. It must be the work of a pirate. Margo scoffs at the idea, but Lamont is serious. This pirate has not been found since there's no one alive to see him. What bothers Lamont more is the pirate's motive; he has preyed on every type of ship from luxury superliners to the common tramp (a type of cargo ship), and the ships' booty has been untouched. Lamont deduces that the pirate must have used a submarine to make him invisible to the ships. The pirate must also be wealthy enough to have that submarine built for him in secrecy, and for that to happen he will need someone to design one. Only a few people in the world can do that. A few secret enquiries at the Naval Department in Washington has yielded a clue: a naval craft designer by the name of Joseph Hart who had been dishonourably discharged from his position. Hart now lives alone in a small house on Oak Road. It is time for The Shadow to pay a visit.

At Hart's house, Hart asks his guest, Barry Vinton, to hand him another bottle of liquor. He does so and Hart pours himself another glass. It is obvious that Hart is getting drunk.Vinton is worried by this, and warns Hart that his drinking will loosen his tongue and cause him to reveal the dangerous secret that they share. Hart assures Vinton that he has not said anything. Vinton still fears he might have a slip of tongue, and tells Hart to pull himself together. Hart cannot. Night after night, he is tormented by nightmares of helpless ships sinking into the depths and the faces of floating corpses. He is racked with guilt for designing and building that submarine for Vinton. Vinton reminds Hart that he was paid well for his services. Hart replies that it was money soaked in blood; he feels responsible for the terror that the insane Vinton has caused.

Hart finally asks Vinton why he has come. Vinton tells him that lately he has been wondering why he let him live; he has become too dangerous to his interests. Hart protests. Vinton tells him that he will spare him if he can prove that their secret is safe, and that he (Hart) can help him in the future. When Hart protests again, Vinton insists that he come aboard the submarine on its next cruise. Hart realises that he will never come back from this particular voyage, and Vinton confirms his fears. But before he leaves Hart in the middle of the sea, he will force him to witness the lethal efficiency of the submarine he designed. Hart begs Vinton to kill him now and get it over with, but Vinton is eager to have him witness his marksmanship as he fires on a terrified crew. Hart protests in vain. Vinton warns him that if he keeps up this attitude, he will request him to "pack his yatching clothes", something which they will both deeply regret.

Vinton leaves, and Hart is left all alone in his despair. The Shadow confronts Hart and offers his help in exchange for revealing his secret. When Hart refuses, The Shadow tells him that he has heard everything that has passed between him and Vinton, and that information is enough to hang him. But Hart still does not think he can do anything. What is done is done. The Shadow tells Hart that his conscience will tell him to do what is right to stop Vinton. Finally, Hart recounts his meeting with Vinton.

Until a year ago, Hart only knew Vinton by his reputation as a millionaire sportsman who enjoyed deep sea fishing and a big game hunting. One day, Vinton came to him seeking a design for a new race boat. From then on, they became friends. Because of this friendship, Hart agreed to build Vinton a submarine, The vessel was built in secret at Vinton's private shipyard out at Kerry's Point. On day of the submarine's launch, Vinton revealed to him what it would truly be used for. Vinton had always been a killer, but big game had lost its appeal, and now he turned to what he regarded as a new sport: the sinking of ships and the killing of the defenceless men on board. Hart was horrified.

The Shadow asks Hart if he knew the exact location of the submarine. Hart does not know; if he knew, he would blow it up and himself with it. Suddenly it hits him. Why should he wait to die at Vinton's hand? He will fool Vinton by doing it himself. No more tortured, sleepless nights for him. No more headlines about another boat being sunk. Vinton will never take him on that voyage. Ever.

Before The Shadow can stop him, Hart pulls out a gun and kills himself.

Later that night, Lamont and Margo drive out to Kerry's Point and park in a desolate spot to avoid being seen. Margo sees a light from the shipyard and notes that the shipyard itself surrounded by a high wall, giving it an eerie look of a prison. Lamont tells her that perhaps it is meant as a prison for those who work in it. He gives Margo instructions to wait until he finds the submarine, after which he will contact her on their private wireless. She will then proceed to contact the US Coast Guard headquarters in Washington and relay his message. The Coast Guard has given their full cooperation in this matter, and will act accordingly. Margo wishes The Shadow good luck.

At the shipyard, two workers named Phil and Charlie lower the last of the torpedoes into the submarine. They notice that the submarine has taken plenty of supplies and ammunition, hence it must be a long tip this time round. Suddenly, one of them hears a noise. It is dismissed as the wind blowing the door shut. Unbeknownst to them, The Shadow has entered the room.

Phil is uneasy. He confides his feelings to Charlie. It seems that they have both been cooped up in the shipyard for three months with no contact with the outside world, not even a newspaper. Phil would rather be back in prison, at least in prison you know when your stay is over and you leave. As far as he's concerned, this shipyard gives him the creeps. The men question Vinton's motives about the submarine. They were told that it was used to hunt whales, but they do not believe the story.

When Vinton comes in to check on their progress, they nervously ask him for a few days off. Vinton refuses their request. They continue to press their case, telling him that though he's paid them well, they haven't had a chance to spend it, and one of them has a wife and child waiting for him. When Vinton refuses again, they threaten to walk out. Vinton merely reminds them of their co-worker, Mr. Hadley, who tried to do the same, but ended up falling from the wall. It turns out it was no accident; he was shot. Phil and Charlie fall silent.

After Vinton leaves, Phil and Charlie have a sinking feeling that they will be here for a very, very long time. The Shadow finally makes himself known and offers them help in exchange for information about the submarine. The men are suspicious at first, but they eventually tell him that the submarine is hidden in an underground berth and it will sail at midnight tonight, heading for Cape Francis. The Shadow immediately informs Margo about Vinton's plans.

The very next morning, we find Vinton in his submarine, searching for his next quarry. His first mate, Mr Brausch, tells him that they are 700 miles due east of Cape Francis, following the shippping lane. The sun has just risen, giving them good visibility. Vinton takes over the submarine's periscope; he is in good spirits for today's hunt. He soon spots something in the water and asks Brausch to take a look. It seems they have found a steam ship, The Orpheus, a luxury liner with a full passenger list including several ambassadors. Vinton orders his crew to increase the submarine's speed, and Brausch to ready the torpedoes. Vinton gleefully looks forward to the kill, and orders the first torpedo to be fired. He eagerly watches as the torpedo heads straight for the ship. Much to his surprise and dismay, the torpedo fails to explode on impact. A dud! Undeterred, Vinton orders a second torpedo to be fired, but it too is a dud. Vinton soon hears The Shadow's mocking laughter. The Shadow reveals that he has sabotaged all of the submarine's torpedos.

Vinton challenges The Shadow and orders the crew to raise the submarine to the surface. If he cannot sink the ship with the torpedoes, the submarine's deck guns will do the trick. The Shadow tells Vinton that he is mad. "Madman, am I? Very well, I'll show you the full extent of my madness!" Vinton replies.

When the submarine has surfaced, Vinton orders the crew to man the guns, and confidently asks The Shadow if he wants to join him up on deck to watch the killing. But it seems The Shadow has beaten him to it. Vinton is annoyed. The Shadow assures Vinton that he will stay near him. Suddenly, one of the crewmen reports that the guns are jammed. Another sabotage by The Shadow! Not to be outfoxed, Vinton orders the crew to ram the ship's hull. The submarine is equiped with a ramming device on its prowl. One blow will sink the ship. The Shadow laughs at Vinton's idea, and tells him that the ship is deserted, filled with explosives and set adrift by the Coast Guard. One blow will send them all to kingdom come. Vinton thinks he is lying. The Shadow tells him that he will find out the truth soon enough; they are about to hit the ship. Vinton quickly tells the crew to put the engine in reverse. The submarine stops just in time, and comes to rest at the ship's side.

Vinton laughs at The Shadow, thinking he has outwitted him, but The Shadow reveals that he now has Vinton exactly where he wants him. He calls out to the Coast Guard, who have been hiding on the ship all along. The Coast Guard board the submarine and arrest the crew.

Vinton dodges the Coast Guard, jumps back into the submarine and shuts the hatch. He heads to the engine room, intending to manouver the dive. As he checks the valves in the engine room, he wonders out loud what The Shadow would be saying up on the submarine's deck. The Shadow replies that it would be pointless for Vinton to make that dive. Vinton is shocked. He pulls out a gun. The Shadow taunts Vinton by revealing that he is in a particular corner of the room. Vinton fires. There is silence. Vinton believes he has killed The Shadow, but The Shadow tells him that he has missed. Infuriated, Vinton begins firing indiscriminately around the room.

The Coast Guard soon burst into the engine room and arrest Vinton. The Shadow mocks Vinton by telling him that his marksmanship is deplorable. Upon hearing The Shadow's voice, one of the Coast Guard asks him who he is. Vinton taunts The Shadow to reveal himself, and calls him a glory-seeker. The Shadow replies that he seeks no glory; his reward is that men and ships can once more safely sail the seas.

The Shadow's work is done.